G20.A2

🧬 ICD-10-CM G20.A2 — Parkinson’s Disease Without Dyskinesia, With Fluctuations

Billable Code Confirmed

ICD-10-CM G20.A2 is a valid, billable 5-character alphanumeric ICD-10-CM code for FY2026. All five characters are present: G20 (category — Parkinson’s Disease) + .A (without dyskinesia) + 2 (with fluctuations/OFF episodes). No 7th character is required. Introduced effective October 1, 2023 (FY2024) as part of the G20 subcategory expansion that retired the single undifferentiated G20 code.

Non-Billable Parent Codes — Never Submit These

• ❌ G20 — The original 3-character code — retired as of FY2024; generates a coding specificity rejection
• ❌ G20.A — 4-character header — non-billable; missing fluctuation specifier

Always submit G20.A2 (all 5 characters) when Parkinson’s disease without dyskinesia AND with documented motor fluctuations or OFF episodes is the diagnosis. Never default to the retired bare G20 when wearing-off or ON-OFF phenomena are documented.

Clinical Context: "With Fluctuations" — What Must Be Documented

G20.A2 requires physician documentation of motor fluctuations — the clinical phenomenon in which levodopa’s therapeutic benefit becomes inconsistent, producing alternating periods of symptom control (ON time) and return of parkinsonian symptoms (OFF time). Per the March 2026 Coding Clinic update (medlearn.com), the ICD-10-CM Alphabetic Index now explicitly cross-references Parkinson’s disease “with OFF episodes” to G20.A2 — OFF episodes = fluctuations. The fluctuations in G20.A2 are present without dyskinesia (no involuntary choreiform/writhing movements). The most common types of fluctuations captured here are:

• End-of-dose wearing-off — predictable return of motor symptoms before the next scheduled dose
• Early-morning akinesia — severe OFF state on awakening before the first morning dose
• Delayed ON — medication takes abnormally long to reach therapeutic effect
• Dose failure / no ON — individual levodopa dose fails to produce any therapeutic response
• Unpredictable ON-OFF switching — abrupt, random fluctuations without relationship to dosing schedule

The absence of dyskinesia (the involuntary movement complication) is what distinguishes G20.A2 from G20.B2 — both have fluctuations, but G20.B2 adds dyskinesia as a concurrent complication.

Code Classification

ICD-10-CM Diagnosis Code — Etiology code under the etiology/manifestation convention. G20.A2 sequences FIRST when Parkinson’s disease dementia is also coded — the F02.x dementia codes are mandatory manifestation codes that sequence second behind G20.A2. For associated inpatient procedure coding, see the ICD-10-PCS Crosswalk section below.

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🔍 Code Description

ICD-10-CM G20.A2 classifies idiopathic Parkinson’s disease at the stage characterized by the emergence of motor fluctuations (OFF episodes, wearing-off phenomena) — a pharmacokinetic and pharmacodynamic complication of long-term levodopa therapy — in the absence of levodopa-induced dyskinesia.

Motor fluctuations develop in the majority of patients with Parkinson’s disease after 3-5 years of levodopa therapy, initially manifesting as end-of-dose wearing-off (the most common and earliest fluctuation type): a predictable, dose-related return of parkinsonian motor and non-motor symptoms in the interval before the next scheduled levodopa dose. As the disease progresses and remaining dopaminergic terminals diminish further, fluctuations become more complex — ON-OFF switching becomes less predictable, OFF periods lengthen and intensify, and the therapeutic window for each levodopa dose narrows. The prevalence of motor fluctuations reaches approximately 40% after 4-6 years and 70% after 9 years of levodopa therapy.

Critically, G20.A2 represents the stage immediately preceding dyskinesia emergence in many patients — while fluctuations are present, receptor hypersensitization has not yet produced the peak-dose or biphasic involuntary movements that define G20.B2 (with dyskinesia AND fluctuations). This stage is clinically important for several reasons: (1) it often triggers advanced therapy evaluation (DBS candidacy assessment, LCIG/CLES pump consideration, subcutaneous apomorphine infusion); (2) it marks the transition to medication regimen complexity that may require frequent neurology visits and pharmacological adjustments; and (3) the presence of documented fluctuations directly supports medical necessity for advanced pharmacological agents (COMT inhibitors: entacapone, opicapone; MAO-B inhibitors: rasagiline, safinamide; extended-release formulations; apomorphine rescue injections) and advanced delivery systems (DBS, LCIG/CLES pump).

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🌳 Code Tree / Hierarchy

G20-G26 Extrapyramidal and Movement Disorders  
│  
├── G20 — Parkinson's Disease ❌ Non-billable (retired as of FY2024)  
│ │ [Excludes1: dementia with Parkinsonism (G31.83)]  
│ │ [Use additional code for dementia]  
│ │  
│ ├── G20.A — PD Without Dyskinesia ❌ Non-billable header  
│ │ ├── G20.A1 — Without dyskinesia, WITHOUT mention of fluctuations ✅ Billable  
│ │ │ [= Stable motor phase; no levodopa motor complications]  
│ │ └── G20.A2 — Without dyskinesia, WITH fluctuations ◀ THIS CODE ✅ Billable  
│ │ [= Wearing-off/OFF episodes present; no dyskinesia yet]  
│ │  
│ ├── G20.B — PD With Dyskinesia ❌ Non-billable header  
│ │ ├── G20.B1 — With dyskinesia, WITHOUT mention of fluctuations ✅ Billable  
│ │ │ [= Dyskinesia present; no wearing-off/OFF episodes documented]  
│ │ └── G20.B2 — With dyskinesia, WITH fluctuations ✅ Billable  
│ │ [= Both dyskinesia AND wearing-off/OFF — most advanced motor complication stage]  
│ │  
│ └── G20.C — Parkinsonism, unspecified ✅ Billable  
│ [Use ONLY when idiopathic vs. secondary cannot be determined]  
│  
├── G21 — Secondary Parkinsonism ← EXCLUDES1 from G20 — separate code family  
│ ├── G21.11 — Neuroleptic induced Parkinsonism ✅ Billable  
│ ├── G21.19 — Other drug induced secondary Parkinsonism ✅ Billable  
│ ├── G21.3 — Postencephalitic Parkinsonism ✅ Billable  
│ ├── G21.4 — Vascular Parkinsonism ✅ Billable  
│ ├── G21.8 — Other secondary Parkinsonism ✅ Billable  
│ └── G21.9 — Secondary Parkinsonism, unspecified ✅ Billable  
│  
└── G22 — Parkinsonism in diseases classified elsewhere ✅ Billable

G20.A2 is the Pivot Point for Advanced Therapy Coding

G20.A2 (no dyskinesia, with fluctuations) is the clinical threshold where advanced therapy eligibility becomes most relevant. When this code is present, ensure the record also captures:

• DBS evaluation/candidacy workup (neuropsychological testing, neurosurgery consultation)
• Trial of or failure with COMT inhibitor (entacapone/opicapone) or MAO-B inhibitor (rasagiline/safinamide)
• Documentation supporting LCIG/CLES pump or subcutaneous apomorphine medical necessity

As the disease progresses further with emergence of dyskinesia, upgrade to G20.B2 (both fluctuations AND dyskinesia). Do not continue coding G20.A2 once dyskinesia is documented.

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✅ Includes

The following clinical terms and scenarios map to G20.A2 when idiopathic Parkinson’s disease is confirmed with documented motor fluctuations and without dyskinesia:

• Parkinson’s disease with end-of-dose wearing-off, no dyskinesia
• Parkinson’s disease with OFF episodes, no dyskinesia
• Parkinson’s disease with on-off phenomenon, no involuntary movements
• Parkinson’s disease with early-morning akinesia (OFF state), no dyskinesia
• Parkinson’s disease with dose failure or delayed ON, no dyskinesia
• Parkinson’s disease with motor fluctuations, without levodopa-induced dyskinesia
• Idiopathic Parkinsonism with wearing-off, pre-dyskinesia stage

Per the March 2026 Coding Clinic update: Parkinson’s disease with “OFF episodes” indexes to G20.A2 — the Alphabetic Index cross-reference for “OFF episodes” as a synonym for fluctuations was formally added, providing authoritative Coding Clinic guidance that “OFF episodes” = fluctuations for G20.A2 assignment.

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❌ Excludes

Excludes 1 — Cannot Be Coded Simultaneously with G20.A2

Code	Description	Note
G21.11	Neuroleptic induced Parkinsonism	Mutually exclusive — dopamine-blocking drug-induced parkinsonism is NOT idiopathic PD; if wearing-off-like symptoms occur in a patient on neuroleptics, idiopathic PD vs. drug-induced Parkinsonism requires physician clarification before G20.A2 is assigned
G21.19	Other drug induced secondary Parkinsonism	Mutually exclusive — code with adverse effect T-code for causative agent; cannot co-exist with G20.A2
G21.3	Postencephalitic Parkinsonism	Mutually exclusive
G21.4	Vascular Parkinsonism	Mutually exclusive — white matter disease-related parkinsonism; no wearing-off in vascular Parkinsonism (no dopaminergic terminal loss to produce fluctuations)
G21.8	Other secondary Parkinsonism	Mutually exclusive
G21.9	Secondary Parkinsonism, unspecified	Mutually exclusive

Excludes 1 — Vascular Parkinsonism Cannot Have Wearing-Off

The Excludes 1 boundary between G20.A2 and G21.4 (vascular Parkinsonism) is clinically important: vascular Parkinsonism (white matter disease, lacunar infarcts producing parkinsonian features) does NOT produce levodopa-responsive wearing-off phenomena because there are no dopaminergic terminals to deplete. If a patient with vascular Parkinsonism is documented as having “wearing-off,” a CDI query is warranted — true wearing-off requires dopaminergic terminal loss (idiopathic PD) as its substrate.

Excludes 2 — May Be Coded in Addition if Separately Present

Code	Description	Note
G31.83	Dementia with Lewy bodies	Excludes 2 from G20 category — may be coded alongside G20.A2 if DLB is distinctly documented alongside idiopathic PD; physician must document both conditions as separately present per clinical criteria

DLB vs. Parkinson's Disease Dementia — The 1-Year Rule

G31.83 (dementia with Lewy bodies) is Excludes 2 from G20, meaning both may be coded when separately documented. The clinical distinction: DLB = dementia onset preceding or within 1 year of motor parkinsonism onset; PDD (G20.A2 + F02.x) = established motor PD documented for >1 year before dementia onset. At the G20.A2 fluctuating stage, PDD becomes increasingly prevalent — document and code dementia severity (F02.Ax/Bx/Cx) and behavioral disturbance type when present.

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📋 Clinical Overview

Understanding Motor Fluctuations — The G20.A2 Clinical Core

Motor fluctuations are not a medication side effect in the traditional sense — they are an intrinsic consequence of progressive dopaminergic neurodegeneration combined with the pharmacokinetics of pulsatile oral levodopa dosing. As stated by Practical Neurology (March 2026), “fluctuations and dyskinesia reflect disease progression, codes that specify treatment consequences are not accurate — OFF episodes are not a result of dose or medication failure and do not indicate that a drug regimen is no longer effective.” This clinical nuance is critical for coder education: G20.A2 is NOT a complication code and does NOT imply medication error, underdosing, or non-adherence.

Fluctuation Type	Clinical Description	Temporal Pattern
End-of-dose wearing-off	Predictable return of PD motor symptoms before next scheduled dose	Dose-related; predictable; most common and earliest type
Early-morning akinesia	Severe OFF state on awakening; symptoms worst before first morning dose	Morning; relieves with first dose
Delayed ON	Medication takes abnormally long (>60 min) to produce therapeutic effect	Post-dose; variable
Dose failure / No ON	Individual levodopa dose fails to produce any therapeutic response	Unpredictable; dose-related
Unpredictable ON-OFF switching	Abrupt, random fluctuations independent of dosing schedule	Unpredictable; advanced stage
Non-motor fluctuations	Pain, anxiety, diaphoresis, cognitive changes cycling with motor ON-OFF	Parallel motor fluctuation timing

CDI Query Trigger — Fluctuation Documentation

The single most impactful CDI action for Parkinson’s disease encounters is asking the neurologist: “Does this patient experience wearing-off or OFF episodes between doses?” If yes and no dyskinesia is present → G20.A2. If both wearing-off and dyskinesia are present → G20.B2. When the neurologist documents only “Parkinson’s disease” without specifying fluctuation status, a query to clarify the motor phase is appropriate, as the distinction is clinically significant for care planning, advanced therapy eligibility, and coding specificity.

G20.A2 as the Advanced Therapy Threshold

The G20.A2 stage represents the clinical inflection point at which standard oral pharmacotherapy becomes insufficient and advanced therapy evaluation is indicated. Documented motor fluctuations without troublesome dyskinesia are the primary eligibility criterion for several key advanced Parkinson’s disease interventions:

Advanced Therapy	Indication at G20.A2 Stage	Relevant CPT/Codes
Deep Brain Stimulation (DBS)	Motor fluctuations responsive to levodopa but not adequately controlled on oral regimen; no dementia; adequate surgical candidacy	61885/61886 (IPG); 95983/95984 (programming)
Levodopa-Carbidopa Intestinal Gel (LCIG/CLES)	Severe motor fluctuations (>3 h/day OFF time) refractory to optimized oral regimen; continuous intrajejunal infusion via PEG/J tube	96365/96366 (infusion); PEG-J tube placement CPT
Subcutaneous apomorphine infusion	Rescue for severe OFF periods; continuous subcutaneous pump	96365/96366 (infusion administration)
COMT inhibitors (entacapone/opicapone)	Extend levodopa effect to reduce wearing-off; first-line pharmacological adjustment for G20.A2	Medication management under E/M visit
MAO-B inhibitors (rasagiline/safinamide)	Reduce OFF time; adjunct to levodopa at fluctuating stage	Medication management under E/M visit
Extended-release carbidopa-levodopa	Smooth out plasma levodopa levels to reduce wearing-off	Medication management under E/M visit

Pathophysiology

At the G20.A2 stage, progressive dopaminergic neurodegeneration has sufficiently depleted nigral terminals that the buffering capacity for exogenous levodopa — the ability of remaining terminals to store, release, and regulate dopamine in a tonic physiological manner — is critically reduced. Oral levodopa’s short plasma half-life (approximately 60-90 minutes for immediate-release formulations) now directly produces pulsatile striatal dopamine signaling that mirrors plasma levodopa peaks and troughs. When plasma levodopa falls below the individual therapeutic threshold before the next dose, dopaminergic receptor stimulation becomes insufficient to suppress PD motor symptoms — producing wearing-off. The striatal dopamine receptors have not yet undergone the hypersensitization that produces peak-dose dyskinesia (G20.B1/G20.B2), which is why G20.A2 is the intermediate stage where fluctuations exist without dyskinesia — a pharmacologically important window for therapeutic adjustment.

Documentation Requirements

For accurate assignment of G20.A2, physician documentation should include:

1. Explicit Parkinson’s disease diagnosis — “Parkinson’s disease,” “idiopathic Parkinson’s disease,” or “PD” by the treating physician
2. Confirmation of idiopathic etiology — no secondary cause documented or suspected
3. Presence of motor fluctuations — explicit documentation of any of: wearing-off, OFF episodes, end-of-dose deterioration, early-morning akinesia, ON-OFF phenomenon, dose failure; per March 2026 Coding Clinic, “OFF episodes” cross-references to G20.A2 in the Alphabetic Index
4. Absence of dyskinesia — no documentation of involuntary choreiform/writhing movements; if dyskinesia is present alongside fluctuations → G20.B2
5. Dementia status — if dementia is present, severity and behavioral disturbance type should be documented for the mandatory F02.x code pair
6. Advanced therapy status — document DBS presence, LCIG/CLES pump, or prior advanced therapy if applicable — critical for device management CPT code support

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💰 HCC Risk Adjustment (CMS-HCC v28)

Field	Detail
CMS-HCC Model Version	v28 (100% Implementation FY2026)
HCC Assignment	✅ Mapped — HCC 155
HCC Category Name	Parkinson’s Disease and Huntington’s Disease
RAF Coefficient (Community Non-Dual Aged)	~0.372
G20 Subcode Differentiation	G20.A2 maps to same HCC 155 as G20.A1/B1/B2 — RAF coefficient is identical across all G20 subcodes
RxHCC Assignment	Review current RxHCC mapping tables

G20.A2 maps to CMS-HCC v28 HCC 155 (Parkinson’s Disease and Huntington’s Disease), the same tier as all other G20 subcodes. The clinical stage of G20.A2 (fluctuating) does not yield a higher RAF than G20.A1 (stable) at the HCC level — but the fluctuating stage is clinically correlated with higher overall comorbidity burden and greater likelihood of RAF-bearing concurrent diagnoses.

Compounding HCC Opportunities — G20.A2 Has Higher Comorbidity Density

At the G20.A2 motor fluctuation stage, the following RAF-bearing comorbidities are significantly more prevalent than at the G20.A1 stable stage, and every encounter should be actively reviewed for completeness:

• Parkinson’s disease dementia (F02.80 through F02.C4) → HCC 125/126/127 — the most impactful stacked HCC; query severity at every visit
• Major depressive disorder (F32.9, F33.9) — highly prevalent at fluctuating stage; non-motor OFF features include severe anxiety and depression
• Dysphagia (R13.19) → review HCC mapping; critical safety code that drives aspiration risk documentation
• Malnutrition (E43, E44.0) → review HCC mapping; increasingly prevalent at advanced PD stages
• Orthostatic hypotension / autonomic dysfunction (G90.3) → review HCC mapping
• Falls — injury codes when applicable

All conditions meeting UHDDS “other diagnoses” criteria must be reported. At the G20.A2 stage, 6-10 active comorbidities is common — complete capture is essential.

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🏥 MS-DRG Assignment

MDC 01 — Diseases and Disorders of the Nervous System

DRG	Title	Est. Relative Weight*
DRG 056	Degenerative Nervous System Disorders with MCC	~2.23
DRG 057	Degenerative Nervous System Disorders without MCC	~1.30

*Approximate. Verify against IPPS FY2026 Final Rule tables. Degenerative nervous system disorders group to only two DRGs — there is no DRG 058 for this pair.

G20.A2 Encounters Have Higher DRG 056 Probability Than G20.A1

Because G20.A2 represents a more advanced disease stage, the comorbidities most likely to elevate to DRG 056 (MCC tier) are more prevalent:

• Severe dementia documented as F02.C0/F02.C1 etc. — MCC
• Aspiration pneumonia (J69.0) — MCC; increasingly likely with progressive dysphagia at fluctuating stage
• Acute respiratory failure (J96.01) — MCC
• Sepsis (A41.9) — MCC

Without active CDI querying for dementia severity, dysphagia, aspiration events, and nutritional status, G20.A2 inpatient cases frequently fall to the significantly lower-weighted DRG 057 — a major reimbursement integrity gap at every Parkinson’s disease inpatient encounter at this stage.

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🔗 Related ICD-10-CM Codes

G20 Subcode Variants — Full Motor Complication Matrix

Code	Description	Motor Stage
G20.A1	Without dyskinesia, without mention of fluctuations	Stable; no motor complications
G20.A2	Without dyskinesia, with fluctuations ← This Code	Wearing-off/OFF present; no dyskinesia
G20.B1	With dyskinesia, without mention of fluctuations	Dyskinesia present; no wearing-off
G20.B2	With dyskinesia, with fluctuations	Both complications — most advanced stage
G20.C1	Parkinsonism, unspecified	Use only when idiopathic vs. secondary undetermined

Secondary Parkinsonism — Excludes1 from G20

Code	Description
G21.11	Neuroleptic induced Parkinsonism
G21.19	Other drug induced secondary Parkinsonism
G21.3	Postencephalitic Parkinsonism
G21.4	Vascular Parkinsonism

Mandatory Associated Codes — Dementia (Use Additional Code per Tabular Instruction)

Code	Description	HCC v28
F02.80	Dementia in other diseases, unspecified severity, without disturbance	HCC 127
F02.A0	Dementia in other diseases, mild, without disturbance	HCC 127
F02.B0	Dementia in other diseases, moderate, without disturbance	HCC 126
F02.C0	Dementia in other diseases, severe, without disturbance	HCC 125
F02.81	Dementia in other diseases, unspecified severity, with behavioral disturbance	HCC 127
F02.B1	Dementia in other diseases, moderate, with behavioral disturbance	HCC 126
F02.C1	Dementia in other diseases, severe, with behavioral disturbance	HCC 125

Common Comorbidity Codes at the G20.A2 Stage

Code	Description	Coding Relevance
G90.3	Multi-system degeneration of the autonomic nervous system	Autonomic dysfunction — orthostatic hypotension, neurogenic bladder, constipation; increasingly prominent at fluctuating stage
R13.19	Other dysphagia	Parkinson’s-related oropharyngeal dysphagia — drives aspiration risk, SLP consult, diet texture modification, aspiration precautions
J69.0	Pneumonitis due to inhalation of food and vomit (aspiration pneumonia)	MCC; the leading cause of death in advanced PD; more prevalent at G20.A2 than G20.A1
G47.52	REM sleep behavior disorder	Highly prevalent at fluctuating stage; important neuropsychiatric comorbidity
F32.9	Major depressive disorder, single episode, unspecified	Non-motor PD comorbidity; mood symptoms may fluctuate with motor ON-OFF
G89.29	Other chronic pain	Musculoskeletal and neuropathic pain is common during OFF episodes — off-related pain is a prevalent non-motor fluctuation; code additionally when documented
W19.XXXA	Unspecified fall, initial encounter	Falls are more frequent at fluctuating stage due to unpredictable motor switching and postural instability during OFF periods
Z96.82	Presence of neurostimulator	Code when DBS device is already implanted at the time of the encounter

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🛠️ Commonly Associated CPT Codes (Neurology)

Outpatient and Physician Setting Context

The CPT codes below are associated with the evaluation, management, and advanced therapy treatment of Parkinson’s disease with motor fluctuations in outpatient and physician fee schedule settings. In the inpatient setting, ICD-10-PCS procedure codes govern procedural reporting.

CPT Code	Description	Clinical Application
99214	Office or other outpatient visit, established patient, moderate MDC	Standard neurology follow-up for G20.A2 motor fluctuation management — medication adjustment (COMT inhibitor addition, levodopa dosing interval change, ER formulation switch); most common E/M level at this stage
99215	Office or other outpatient visit, established patient, high MDC	Complex fluctuation management — DBS candidacy evaluation, advanced therapy counseling (LCIG, apomorphine), caregiver burden with non-motor fluctuations, polypharmacy adjustment
99483	Cognitive assessment and care plan services	Annual or episodic formal cognitive assessment — Parkinson’s disease dementia (PDD) becomes increasingly prevalent at the fluctuating stage; all 9 elements required; modifier -25 required if same DOS as standard E/M
96132	Neuropsychological testing evaluation; first hour	DBS candidacy evaluation — neuropsychological battery is a standard prerequisite for DBS surgical candidacy at the G20.A2 fluctuating stage; also used for PDD staging and DLB vs. PDD differentiation
96133	+Neuropsychological testing evaluation; each additional hour	Add-on; never alone
96116	Neurobehavioral status exam; first hour	Office-based structured cognitive assessment — screening for emerging PDD at the fluctuating stage; MoCA, MMSE, MDS-UPDRS cognitive subscale
95983	Electronic analysis of implanted neurostimulator pulse generator/transmitter (DBS), programming; first 15 minutes	DBS programming — for G20.A2 patients with existing DBS managing motor fluctuations through stimulation parameter adjustment; requires in-person or telehealth interaction
95984	+Electronic analysis of implanted neurostimulator pulse generator/transmitter (DBS), programming; each additional 15 minutes	Add-on for additional DBS programming time; never alone
61885	Insertion or replacement of cranial neurostimulator pulse generator; connection to single electrode array	DBS IPG implantation or replacement (battery change); G20.A2 motor fluctuations support DBS medical necessity
61886	Insertion or replacement of cranial neurostimulator pulse generator; connection to two or more electrode arrays	Bilateral DBS IPG implantation — most common PD DBS configuration (bilateral STN or GPi)
96365	Intravenous infusion for therapy; initial, up to 1 hour	Report for continuous enteral/infusion administration of carbidopa-levodopa suspension (CLES/LCIG) or subcutaneous apomorphine infusion in outpatient/clinic settings when administered by qualified healthcare personnel
96366	+Intravenous infusion, each additional hour	Add-on for each additional hour of infusion; never alone

NCCI Bundling Considerations

NCCI PTP Edits — Verify Before Billing

• 95983 and 95984 are time-based: 95983 = first 15 minutes; each 95984 = additional 15 minutes. Both are bundled into DBS surgical procedure codes (61885/61886) on the same DOS — do NOT report programming with implantation.
• 99215 (complex E/M) on the same DOS as 95983/95984 DBS programming: modifier -25 must be appended to the E/M when the E/M is a separately identifiable service beyond the programming visit itself.
• 99483 (cognitive assessment) and a standard E/M same DOS: modifier -25 required on the E/M.
• 96132 (neuropsychological testing) and 95983 (DBS programming) same DOS: verify NCCI PTP edit status; documentation must clearly distinguish each service as separately medically necessary and independently performed.
• 61885 or 61886 (IPG implant/replacement) and 95983 same DOS: bundled — do NOT report DBS programming on the same day as surgical IPG implantation.

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🔬 ICD-10-PCS Crosswalk (Inpatient Procedures)

When G20.A2 is an inpatient diagnosis and a surgical or therapeutic procedure is performed, the following ICD-10-PCS sections and root operations are relevant. Full PCS codes require completion of all seven characters — consult the PCS tables for the applicable fiscal year.

PCS Section	Body System	Root Operation	Clinical Application
0 (Medical & Surgical)	0 (Central Nervous System)	H (Insertion)	00H00MZ — DBS lead placement (open, brain — STN or GPi target); G20.A2 fluctuating PD is a primary DBS indication
0 (Medical & Surgical)	J (Subcutaneous Tissue)	H (Insertion)	0JH60MZ — DBS IPG implantation (chest subcutaneous tissue)
0 (Medical & Surgical)	D (Gastrointestinal)	H (Insertion)	0DH64UZ — PEG/J tube insertion for LCIG/CLES infusion access; reported when J-tube placed for carbidopa-levodopa intestinal gel delivery in advanced fluctuating PD
0 (Medical & Surgical)	0 (Central Nervous System)	W (Revision)	DBS lead revision or IPG replacement — revision root operation when device is revised or battery exchanged
G (Mental Health)	Z (None)	3 (Psychological Tests)	GZ3ZZZZ — Neuropsychological testing for DBS candidacy assessment in inpatient setting

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💊 Coding Scenarios and Examples

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Scenario 1 — Parkinson’s Disease With Wearing-Off, No Dyskinesia, Medication Adjustment (Outpatient)

Clinical Vignette: A 69-year-old female with Parkinson’s disease on levodopa/carbidopa for 4 years presents reporting that her medications “wear off” approximately 45 minutes before each dose. She experiences return of tremor and stiffness in the OFF intervals. No involuntary movements (no dyskinesia). Physician adjusts dosing schedule and adds entacapone (COMT inhibitor) to extend levodopa duration. Documents: “Parkinson’s disease with wearing-off, no dyskinesia.”

CPT Codes (Outpatient/Physician):

• 99214 — Office visit, established patient, moderate MDC (medication adjustment, complication management)

ICD-10-CM:

• G20.A2 — Parkinson’s disease without dyskinesia, with fluctuations (wearing-off = fluctuations; no dyskinesia)

Wearing-Off Documentation = G20.A2

Any of these physician terms map to G20.A2: “wearing-off,” “end-of-dose deterioration,” “OFF episodes,” “ON-OFF phenomenon,” “motor fluctuations,” “dose failure” — all without concurrent dyskinesia. Per March 2026 Coding Clinic, the Alphabetic Index explicitly cross-references “OFF episodes” → G20.A2.

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Scenario 2 — DBS Candidacy Evaluation, Parkinson’s Disease With Fluctuations (Outpatient)

Clinical Vignette: A 64-year-old male with PD with motor fluctuations (wearing-off, early-morning akinesia) — no dyskinesia — is referred for DBS candidacy evaluation. Neuropsychological testing is ordered to assess cognitive eligibility for surgery. Visit documents: “Parkinson’s disease with motor fluctuations, no dyskinesia; evaluating for DBS candidacy.”

CPT Codes:

• 99215 — Office visit, established patient, high MDC (DBS candidacy evaluation, advanced therapy counseling); append modifier -25 if neuropsychological testing is initiated same day
• 96132 — Neuropsychological testing evaluation; first hour (DBS candidacy cognitive assessment — standard prerequisite)

ICD-10-CM:

• G20.A2 — Parkinson’s disease without dyskinesia, with fluctuations

G20.A2 Supports DBS Medical Necessity

Motor fluctuations (G20.A2 or G20.B2) documented as inadequately controlled on optimized oral therapy are the primary ICD-10-CM codes supporting DBS medical necessity on prior authorization and LCD/NCD documentation checklists. G20.A1 (no fluctuations) does not support DBS medical necessity as strongly as G20.A2.

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Scenario 3 — Parkinson’s Disease With Fluctuations, Dementia, DRG 056 (Inpatient)

Clinical Vignette: A 76-year-old male with Parkinson’s disease with wearing-off and early-morning akinesia (no dyskinesia) is admitted for worsening motor fluctuations and aspiration pneumonia. He has moderate-severity Parkinson’s disease dementia with behavioral disturbance (agitation, visual hallucinations). Physician documents: “PD with motor fluctuations, no dyskinesia; moderate PDD with behavioral disturbance; aspiration pneumonia due to PD dysphagia.”

Principal Diagnosis:

• G20.A2 — Parkinson’s disease without dyskinesia, with fluctuations (etiology — sequences first)

Additional Diagnoses:

• F02.B1 — Dementia in other diseases, moderate severity, with behavioral disturbance (mandatory F02.x manifestation pair)
• J69.0 — Aspiration pneumonia (MCC — drives DRG 056)
• R13.19 — Other dysphagia (supporting comorbidity)

MS-DRG Assignment:

• DRG 056 — Degenerative Nervous System Disorders with MCC (J69.0 as MCC)

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Scenario 4 — G20.A2 With Existing DBS, Routine Programming (Outpatient)

Clinical Vignette: A 71-year-old female with Parkinson’s disease with fluctuations (wearing-off, early-morning akinesia; no dyskinesia), status post bilateral STN DBS implantation 2 years ago, presents for DBS programming. Motor fluctuations persist despite DBS and require stimulation parameter adjustment. Programming takes 30 minutes total.

CPT Codes:

• 99213 — Office visit, established patient, low MDC; append modifier -25
• 95983 — DBS programming, first 15 minutes
• 95984 — +DBS programming, each additional 15 minutes (×1)

ICD-10-CM:

• G20.A2 — Parkinson’s disease without dyskinesia, with fluctuations
• Z96.82 — Presence of neurostimulator (code additionally for existing DBS device)

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⚠️ Coding Pitfalls and Tips

	Pitfall or Tip
❌	Do not submit the retired bare G20 code — non-billable since FY2024; always use a 5-character G20 subcode
❌	Do not use G20.A1 when fluctuations are documented — any documented wearing-off, OFF episodes, or ON-OFF phenomenon requires upgrade to G20.A2; continuing to code G20.A1 when fluctuations have emerged undercodes disease stage
❌	Do not use G20.A2 when dyskinesia is also documented — once dyskinesia appears alongside fluctuations, the correct code is G20.B2 (both dyskinesia AND fluctuations); G20.A2 is reserved for fluctuations without dyskinesia only
❌	Do not code G20.A2 for vascular Parkinsonism or drug-induced Parkinsonism — these are secondary forms (G21.x), Excludes1 from G20; true wearing-off requires dopaminergic terminal loss, which is absent in secondary Parkinsonism
❌	Do not sequence F02.x as principal — Parkinson’s dementia codes are mandatory manifestation codes; G20.A2 always sequences first when the G20.A2 + F02.x pair is coded
❌	Do not omit the F02.x code when PDD is documented — the “Use additional code” instruction is mandatory; missing the dementia code loses HCC 125/126/127 capture and understates clinical complexity
❌	Do not report 95983/95984** on the same DOS as 61885/61886 DBS surgery** — intraoperative/immediate post-implant programming is bundled into the surgical procedure codes
✅	Always query: “Are fluctuations present? Is dyskinesia present?” — these two questions determine the correct G20 subcode at every Parkinson’s disease encounter
✅	Query for dementia severity at every G20.A2 encounter — PDD prevalence rises sharply at the fluctuating stage; F02.Bx (moderate → HCC 126) or F02.Cx (severe → HCC 125) is more impactful than defaulting to F02.80 (unspecified → HCC 127)
✅	Code Z96.82 (presence of neurostimulator) when DBS is already implanted — supports medical necessity for programming visits and advanced therapy management
✅	Code dysphagia (R13.19) and aspiration pneumonia (J69.0) whenever documented — dysphagia is more prevalent at the fluctuating stage; aspiration pneumonia is MCC and drives DRG 056
✅	Document and code non-motor fluctuations — pain, anxiety, depression, cognitive changes cycling with motor ON-OFF should be captured with appropriate codes (G89.29 pain, F32.9 depression) when documented as active conditions
✅	G20.A2 supports advanced therapy medical necessity — when coding for DBS candidacy evaluation, LCIG pump initiation, or apomorphine infusion, G20.A2 directly supports medical necessity; ensure the code is specificity-appropriate before submission

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📚 Sources

1. CMS/NCHS. ICD-10-CM Official Guidelines for Coding and Reporting, FY2026. Tabular List — G20.A2; G20.A subcategory structure; Use additional code instructions; Etiology/Manifestation Convention (Section I.B.13).

2. AHA Coding Clinic (via medlearn.com). Coding Update: An Index Change for Parkinson’s Disease. March 2026. Official Alphabetic Index update cross-referencing “OFF episodes” to G20.A2.

3. Practical Neurology. Parkinson Disease ICD-10-CM Coding. Published March 2026. Clinical and coding context for dyskinesia/fluctuation subcode distinctions; clarification that motor complications are disease progression, not medication error.

4. Stanford Medicine Parkinson’s Disease Clinic. Motor Fluctuations and OFF Times in Parkinson’s Disease. Published December 2025. Clinical description of wearing-off types.

5. Parkinson’s Foundation. Motor Fluctuations and Parkinson’s “Off” Times. Patient and clinical education resource on ON-OFF phenomenon.

6. PMC/NIH. Motor and Non-Motor Fluctuations in Parkinson’s Disease. PMC12855397. Published July 2025. Comprehensive classification of fluctuation types.

7. CMS. 2026 Medicare Advantage CMS-HCC Model v28 — Final Risk Adjustment Coefficients. HCC 155 (Parkinson’s Disease and Huntington’s Disease).

8. CMS. IPPS Final Rule FY2026 — MS-DRG Definitions Manual v43. MDC 01; DRG 056/057.

9. Boston Scientific. Deep Brain Stimulation 2026 Reimbursement Guide. CPT codes 95983/95984/61885/61886 for G20.A2 medical necessity.

10. AMA. CPT Professional Edition 2026. Neurology; DBS programming; neuropsychological testing codes.

11. CMS. NCCI Policy Manual for Medicare Services, current version. Neurology/neurosurgery correct coding.