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G70.00

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ICD-10-CM G70.00: Myasthenia Gravis Without (Acute) Exacerbation

Quick reference

ElementValue
ICD-10-CM codeG70.00
Official descriptorMyasthenia gravis without (acute) exacerbation
SynonymMyasthenia gravis NOS (not otherwise specified)
Parent categoryG70.0 - Myasthenia gravis; G70 - Myasthenia gravis and other myoneural disorders
ICD-10-CM chapterG00 -G99 (Diseases of the nervous system) → G70 -G73 (Diseases of myoneural junction and muscle)
Billable✓ Yes (terminal, reportable code)
Clinical mechanismAutoimmune attack on acetylcholine receptors at neuromuscular junction causing fatigable muscle weakness
HCC statusYES - HCC-relevant in CMS-HCC models (verify current-year V28 mapping; previously mapped in risk adjustment models)
Chronic conditionYes (autoimmune neuromuscular disorder requiring ongoing management)
Annual recapture requiredYES - HCC codes must be recaptured annually for risk adjustment; resets each January

Short description

G70.00 codes myasthenia gravis without acute exacerbation - a chronic autoimmune neuromuscular disorder characterized by fatigable weakness of skeletal muscles that worsens with activity and improves with rest, in a patient who is not currently experiencing myasthenic crisis or acute worsening requiring hospitalization or intensive intervention.

Tip

Use G70.00 when the patient’s myasthenia gravis is stable, controlled, or in the chronic maintenance phase (not in acute crisis).

Full description (clinical context)

Pathophysiology of myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease affecting the neuromuscular junction where nerves communicate with muscles.

Mechanism:

  • Autoantibodies (most commonly IgG1 and IgG3) attack nicotinic acetylcholine receptors (AChR) on the postsynaptic muscle membrane.
  • Antibody binding blocks acetylcholine from binding to receptors and triggers complement-mediated destruction of the receptors.
  • Reduced functional receptors → impaired neuromuscular transmission → muscle weakness.
  • In some patients, antibodies target muscle-specific kinase (MuSK) or other neuromuscular junction proteins instead of AChR.

Fatigability is the hallmark:

  • Muscle weakness worsens with repeated use and improves with rest.
  • Symptoms typically worse later in the day (end-of-day fatigue).
  • Painless muscle weakness (distinguishes from myalgia/myositis).

Clinical presentation & symptoms

Most common initial presentation: Ocular symptoms (50 -90% of patients)

  • Ptosis (drooping eyelids) - often asymmetric; worse with sustained upgaze.
  • Diplopia (double vision) - from extraocular muscle weakness.
  • Ocular myasthenia: Symptoms limited to eyes for ≥2 years; ~85% who don’t generalize by 2 -3 years remain ocular-only.

Generalized myasthenia gravis (progresses from ocular or starts as generalized):

  • Bulbar symptoms: Dysphagia (difficulty swallowing), dysarthria (slurred speech), difficulty chewing, nasal regurgitation.
  • Limb weakness: Proximal > distal (trouble lifting arms overhead, climbing stairs, rising from chair).
  • Neck weakness: Head drop (difficulty holding head up).
  • Facial weakness: Expressionless face, weak smile.
  • Respiratory muscle weakness: In severe cases, can progress to myasthenic crisis (respiratory failure requiring intubation - code G70.01).

Classic MG exam findings:

  • Ptosis that worsens with sustained upgaze (60-second test).
  • Ice pack test positive: Applying ice to closed eyelid for 2 minutes improves ptosis (cold slows acetylcholinesterase, prolonging ACh availability).
  • Cogan’s lid twitch: Rapid upward overshoot of upper eyelid when patient looks up after sustained downgaze.
  • Normal deep tendon reflexes (distinguishes from myopathy/neuropathy).
  • Normal sensation (pure motor disorder).

Diagnostic criteria & workup

Serologic testing:

  • Anti-AChR antibodies: Positive in ~85% of generalized MG, ~50% of ocular MG.
  • Anti-MuSK antibodies: Positive in ~40% of AChR-negative MG (more common in women, tends to have bulbar predominance).
  • Anti-LRP4 antibodies: Rare; in some seronegative patients.

Electrodiagnostic testing:

  • Repetitive nerve stimulation (RNS): ≥10% decrement in compound muscle action potential (CMAP) amplitude between 1st and 4th/5th stimuli at 2 -3 Hz stimulation = abnormal; suggests neuromuscular junction defect.
  • Single-fiber EMG: Most sensitive test; shows increased jitter (variability in time between muscle fiber action potentials); abnormal in >95% of generalized MG.

Pharmacologic testing:

  • Tensilon test (edrophonium test): CPT 95857 - IV edrophonium (short-acting cholinesterase inhibitor) transiently improves weakness if MG present; must have atropine available for cholinergic side effects.
  • Less commonly used now due to availability of serologic testing.

Imaging:

  • Chest CT or MRI: Screen for thymoma (present in 10 -15% of MG patients) or thymic hyperplasia; important because thymectomy is indicated for thymoma.

Subtypes & classification

SubtypeDescriptionKey features
Ocular MGWeakness limited to eyelids/extraocular musclesPtosis, diplopia; may remain localized or progress to generalized
Generalized MGLimb, bulbar, and/or respiratory muscle involvementMost common form; includes varying severity
Thymoma-associated MGMG + thymic tumor10 -15% of MG; thymectomy indicated
Seronegative MGAChR and MuSK antibody-negative~10 -15% of patients; may have LRP4 or other antibodies

Coding specifics (G70.00 vs G70.01)

Code structure breakdown

Character positionValueMeaning
1stGDiseases of the nervous system
2nd -3rd70Myasthenia gravis and other myoneural disorders
4th.0Myasthenia gravis
5th -6th0Without (acute) exacerbation

When to code G70.00

Use G70.00 when:

  • Patient has confirmed myasthenia gravis (serologic or clinical diagnosis).
  • MG is stable, controlled, or in maintenance phase.
  • Patient is on chronic therapy (pyridostigmine, immunosuppressants, IVIG, etc.) without acute crisis.
  • Outpatient management or routine follow-up visits.
  • No current myasthenic crisis or acute respiratory compromise.

Supporting documentation phrases:

  • “Myasthenia gravis, stable on current therapy.”
  • “MG without acute exacerbation, continues pyridostigmine and prednisone.”
  • “Chronic myasthenia gravis, currently well-controlled.”
  • “Generalized MG, no recent exacerbations.”

When to code G70.01 (WITH acute exacerbation) instead

Use G70.01 when:

  • Myasthenic crisis: Severe generalized weakness with respiratory failure requiring mechanical ventilation.
  • Acute worsening requiring hospital admission, IVIG, or plasmapheresis.
  • Significant clinical decompensation from baseline MG status.

Key distinction: G70.00 = chronic/stable; G70.01 = acute crisis/severe exacerbation.

ICD-10-CMDescriptionWhen to use
G70.0Myasthenia gravis (category)Non-billable parent
G70.00Myasthenia gravis without (acute) exacerbationStable/chronic (THIS)
G70.01Myasthenia gravis with (acute) exacerbationMyasthenic crisis/acute worsening
G70.1Toxic myoneural disordersDrug-induced NMJ disorder
G70.2Congenital and developmental myastheniaCongenital MG syndromes
G70.8xOther specified myoneural disordersLambert-Eaton, etc.
G70.9Myoneural disorder, unspecifiedAvoid when MG confirmed
P94.0Transient neonatal myasthenia gravisNeonatal only (Excludes1)

Excludes1 notes (from G70 category)

Do not use G70.00 for:

  • Botulism (A05.1,A48.51, A48.52) - different neuromuscular toxin mechanism.
  • Transient neonatal myasthenia gravis (P94.0) - temporary condition in newborns of MG mothers; use P94.0 instead.

HCC information (risk adjustment) - CRITICAL FOR CODING

HCC status: YES - G70.00 is HCC-relevant

G70.00 myasthenia gravis maps to HCC categories in CMS-HCC risk adjustment models.

CMS-HCC Model evolution:

  • V24 (2020 model): 86 HCC categories; used through 2023.
  • V28 (2024 model): 115 HCC categories (expanded); began phased implementation in 2024.
  • 3-year transition (2024 -2026): Blended risk scores calculated from both V24 and V28. <
    • Payment Year 2024: 67% V24 + 33% V28
    • Payment Year 2025: 50% V24 + 50% V28
    • Payment Year 2026: 33% V24 + 67% V28 (full V28 implementation)

Why this matters for G70.00:

  • Annual recapture required: HCC codes reset every January 1st; must be documented at least once per calendar year (preferably at annual wellness visit or comprehensive exam) to maintain RAF score.
  • RAF impact: Neuromuscular disorders like MG increase predicted healthcare costs; HCC status increases reimbursement to MA plans.
  • Documentation specificity: Must document “myasthenia gravis” explicitly—cannot infer from just “muscle weakness” or “ptosis.”

Best practice for HCC capture:

  • Document “Myasthenia gravis, stable” or “MG without acute exacerbation” at annual exams and major E/M visits.
  • Include MG on problem list with HCC at top if not using specialty default.
  • Code G70.00 at any applicable encounter where MG is addressed (E/M visits); not restricted to neurology visits.
  • Ensure ICD-10 is from physician encounter (E/M codes) for HCC acceptance.

Documentation requirements (work checklist)

Essential elements for G70.00

To support accurate coding, HCC capture, and medical necessity:

  1. Explicit diagnosis statement

    • “Myasthenia gravis” or “MG” stated clearly in assessment.
    • Specify “without acute exacerbation” or “stable” to justify G70.00 vs G70.01.

  2. Diagnostic confirmation documented (at some point in record)

    • Positive AChR antibodies, MuSK antibodies, or other antibody testing.
    • Abnormal RNS or single-fiber EMG results.
    • Positive Tensilon test (if performed).
    • Clinical diagnosis based on characteristic fatigable weakness pattern.

  3. Subtype/severity classification (helpful for care planning)

    • Ocular vs generalized MG.
    • Thymoma-associated (if applicable).
    • Seronegative (if antibody-negative).

  4. Current symptom status

    • “Stable ptosis and diplopia.”
    • “No recent exacerbations or respiratory compromise.”
    • “Muscle strength adequate for activities of daily living.”

  5. Current treatment regimen

    • Medications: pyridostigmine (Mestinon), prednisone, azathioprine, mycophenolate, rituximab, IVIG, etc.
    • Document compliance and response.
    • Post-thymectomy status (if applicable).

  6. Functional impact

    • Ocular symptoms (ptosis, diplopia).
    • Bulbar symptoms (dysphagia, dysarthria).
    • Limb weakness interfering with ADLs.

  7. Monitoring parameters

    • Recent exacerbations or hospitalizations.
    • Medication side effects (especially steroids).
    • Respiratory function if generalized MG.

Common auditor red flags

  • “Muscle weakness” or “ptosis” without “myasthenia gravis” stated → cannot code G70.00; need explicit diagnosis.
  • No documentation of MG in current year → HCC not recaptured; RAF score drops.
  • Chart note says “MG exacerbation” or “myasthenic crisis” but G70.00 (without exacerbation) coded → incorrect code; use G70.01.
  • Drug-induced myasthenic symptoms (e.g., from statins, penicillamine, ICIs) coded as G70.00 → query provider; may be G70.1 (toxic myoneural disorder) or drug-specific code.

Associated CPT codes (common pairings)

E/M codes (HCC capture opportunities)

CPTDescriptionContext for G70.00
99202 -99205New patient office visitInitial neurology consult for MG diagnosis
99212 -99215Established patient visitRoutine MG follow-up; HCC capture visits
99395 -99397Preventive medicine, establishedAnnual wellness visit - IDEAL for HCC recapture
99341 -99345Home visits, new patientHouse calls for disabled MG patients
99347 -99350Home visits, establishedOngoing home-based MG management

Diagnostic testing (MG workup & monitoring)

| CPT | Description | Clinical use | Notes | |---|---|---| | 95857 | Tensilon test (edrophonium challenge) | MG diagnostic confirmation [1072][1075] | IV edrophonium; requires atropine standby; less common now due to antibody testing | | 95860 -95864 | Needle EMG (1 -4 extremities) | Single-fiber EMG showing increased jitter = most sensitive MG test [1055] | Requires neuromuscular specialist | | 95885 | Needle EMG, limited | Limited EMG for MG evaluation | Used in targeted settings | | 95937 | Neuromuscular junction testing (repetitive stimulation) | RNS showing ≥10% decrement = abnormal [1047] | Standard electrodiagnostic test for MG | | 86255 | Antibody; acetylcholine receptor (AChR) | Serologic confirmation of MG [1055] | Positive in ~85% generalized MG | | 86336 | Antibody; muscle-specific kinase (MuSK) | MuSK-MG testing [1047] | For AChR-negative patients | | 71260 | CT chest with contrast | Screen for thymoma [1073] | Indicated in all MG patients | | 71550 | MRI chest without contrast | Alternative thymoma screening | Better soft tissue resolution | | 94010 | Spirometry | Respiratory function monitoring | Important in generalized MG | | 94200 | Maximum breathing capacity (MBC) | Respiratory muscle strength | Used in MG respiratory assessment |

CPTDescriptionMG treatment context
96365 -96368IV infusion (first hour + each additional hour)IVIG infusion for MG
96374IV push, single or initialRapid medication administration
36514 -36516Therapeutic apheresisPlasmapheresis for MG crisis or severe exacerbations
J1459Injection, immune globulin (Privigen), IVIVIG HCPCS code
J9999Not otherwise classified, drugMay be used for certain biologics

Surgical CPT (if thymectomy performed)

CPTDescriptionMG surgical treatment
32673Thoracoscopic thymectomyMinimally invasive thymectomy for nonthymomatous MG
60520Thymectomy, partial or total; transcervicalTranscervical approach
60521Thymectomy, partial or total; sternal split or transthoracicExtended transsternal thymectomy (landmark MGTX trial approach) [1073][1076]
60522Thymectomy, partial or total; sternal split with radical mediastinal dissectionFor thymoma with extension

Treatment overview (coding context)

Pharmacologic management (document for medical necessity)

Symptomatic treatment:

  • Pyridostigmine (Mestinon): Cholinesterase inhibitor; first-line symptomatic therapy; typical dose 30 -120 mg PO q4 -6h.
  • Most patients don’t need pyridostigmine long-term once immunotherapy achieves control. [1076]

Immunosuppressive therapy: [1073][1076]

  • Prednisone: Most common; start low-dose or high-dose depending on severity; taper slowly to maintenance dose (goal <10 mg every other day).
  • Steroid-sparing agents: Azathioprine, mycophenolate mofetil, cyclosporine, tacrolimus.
  • Biologics: Rituximab (anti-CD20), eculizumab (complement inhibitor for refractory MG), efgartigimod (FcRn blocker).

Acute exacerbation treatment (G70.01): [1047]

  • IVIG (0.4 g/kg/day × 5 days) or plasmapheresis for myasthenic crisis or severe worsening.

Thymectomy (surgical management)

Indications: [1065][1073][1076]

  • Thymoma-associated MG: Mandatory (tumor removal + improve MG).
  • Nonthymomatous MG: Recommended for AChR-positive MG patients age 18 -65 with <5 years disease duration.
    • MGTX trial: Thymectomy + prednisone vs prednisone alone → 88% vs 54% achieved minimal manifestation status at 5 years. [1073]
    • Thymectomy group had lower prednisone doses and fewer hospitalizations.
  • Benefits: 30% complete remission; 60% significant improvement; reduced immunosuppression requirements. [1065]

Sample ICD-10 combinations (work scenarios)

Scenario 1: Stable generalized MG on chronic therapy

ICD-10-CM codes:

  • G70.00 - Myasthenia gravis without (acute) exacerbation
  • H02.422 - Myogenic ptosis of left eyelid (if ptosis documented as current problem)
  • H53.40 - Visual field defects (if functional visual impairment documented)
  • Z79.51 - Long-term use of steroids (if on chronic prednisone)

CPT: 99214 (established patient visit, moderate complexity)

Rationale: Captures both primary diagnosis (G70.00 for HCC) and manifestations; Z79.51 documents chronic steroid use (important for monitoring side effects).

Scenario 2: MG patient presenting for annual wellness visit (HCC recapture)

ICD-10-CM codes:

  • Z00.00 - Encounter for general adult medical exam without abnormal findings (primary for AWV)
  • G70.00 - Myasthenia gravis without (acute) exacerbation (HCC recapture)
  • E11.9 - Type 2 diabetes mellitus without complications (if applicable)
  • I10 - Essential hypertension (if applicable)

CPT: 99397 (preventive medicine, established patient, age-appropriate)

Rationale: Annual wellness visits are IDEAL for HCC recapture; list all active chronic conditions to maintain RAF scores. [1056]

Scenario 3: Post-thymectomy MG patient in remission (still code G70.00)

ICD-10-CM codes:

  • G70.00 - Myasthenia gravis without (acute) exacerbation
  • Z98.89 - Other specified postprocedural states (thymectomy status)

CPT: 99213 (follow-up visit)

Rationale: Even if in remission/minimal symptoms, MG is a lifelong diagnosis; continue coding G70.00 annually for accurate HCC capture unless provider explicitly documents “resolved.” [1056]

Scenario 4: New-onset MG diagnosis (initial workup)

ICD-10-CM codes:

  • G70.00 - Myasthenia gravis without (acute) exacerbation
  • H02.421 - Myogenic ptosis of right eyelid
  • H53.122 - Diplopia

CPT:

  • 99204 (new patient visit, high complexity)
  • 95857 (Tensilon test, if performed)
  • 86255 (AChR antibody test)
  • 71260 (CT chest with contrast for thymoma screening)

Rationale: Establishes new MG diagnosis with supporting tests; captures manifestations. [1072][1075]

Sample documentation (clinic note template)

Chief Complaint: Myasthenia gravis follow-up.

HPI: [Age]-year-old [male/female] with myasthenia gravis diagnosed [timeframe] presenting for routine follow-up. MG is currently stable without acute exacerbation. Patient reports [current symptoms: mild ptosis OD, no diplopia / occasional dysphagia / no recent exacerbations]. [Compliance with medications]. No recent hospitalizations for MG. No respiratory symptoms or dyspnea.

Past Medical History:

  • Myasthenia gravis (diagnosed [date]; AChR antibody-positive / MuSK-positive / seronegative; ocular / generalized)
  • Status post thymectomy [date] (if applicable)
  • [Other chronic conditions for HCC capture]

Current Medications:

  • Pyridostigmine (Mestinon) [dose] PO [frequency]
  • Prednisone [dose] PO daily/every other day
  • [Other immunosuppressants: azathioprine, mycophenolate, etc.]

Exam:

  • Ocular: Ptosis [present/absent; if present, degree and laterality]; diplopia [present/absent]; extraocular movements [full/limited]
  • Bulbar: Speech [normal/dysarthric]; swallow function [normal/dysphagia noted]
  • Motor: Proximal muscle strength [normal/reduced]; neck flexor strength [normal/weak]; fatigability with repetitive testing [present/absent]
  • Respiratory: Clear breath sounds; no respiratory distress; [spirometry results if done]
  • Neurologic: Reflexes normal; sensation intact

Assessment:

  • Myasthenia gravis without (acute) exacerbation, stable on current therapy [ocular / generalized; AChR-positive / MuSK-positive / seronegative] [1052][1054]
  • [Other diagnoses]

Plan:

  • Continue current MG medications; no dose adjustments needed.
  • Monitor for exacerbations; patient educated on myasthenic crisis warning signs (respiratory difficulty, severe dysphagia, severe generalized weakness).
  • Monitor for steroid side effects (if on prednisone); DEXA scan for osteoporosis screening (if long-term steroid use).
  • Follow-up in [timeframe] or sooner if symptoms worsen.
  • [If due for testing: Consider repeat antibody titers, EMG, chest CT for thymoma surveillance]

ICD-10-CM:

  • G70.00 - Myasthenia gravis without (acute) exacerbation
  • [H02.421/422/423 - Myogenic ptosis, if present]
  • [Z79.51 - Long-term steroid use, if applicable]
  • [Other chronic conditions for HCC]

CPT:

  • 99214 - Established patient office visit, moderate complexity [or appropriate E/M level]
  • [Other procedures/tests if performed]

Billing & compliance pearls

  • G70.00 is HCC-relevant - must be documented at least once per calendar year to maintain RAF score; preferably at annual wellness visit or comprehensive exam. [1056][1071]
  • Explicit “myasthenia gravis” required - cannot code from just “ptosis,” “diplopia,” or “muscle weakness” without stated diagnosis. [1056]
  • Distinguish G70.00 vs G70.01 - stable/chronic = G70.00; acute crisis/exacerbation = G70.01. [1058]
  • Problem list optimization - Place G70.00 at top of problem list (if not using specialty default) to ensure visibility and annual recapture. [1056]
  • E/M visits qualify for HCC capture - any physician encounter with E/M code can capture G70.00; not limited to neurology. [1056]
  • Document treatment compliance and response - supports medical necessity for ongoing medications, IVIG, plasmapheresis, or thymectomy. [1057][1073]
  • Code manifestations separately - ptosis (H02.42x), diplopia (H53.12), dysphagia (R13.x) can be coded in addition to G70.00 for complete clinical picture. [1055]

Key sources (compact format)

[1047]: Myasthenia gravis pathophysiology, symptoms, autoimmune mechanism, AChR antibodies, ocular/generalized subtypes, ice pack test, Cogan’s lid twitch, treatment overview
[1052]: AAPC G70.00 official descriptor, category hierarchy, Excludes1 notes
[1051]: ECGWaves G70.00 classification under G70 -G73 diseases of myoneural junction
[1054]: Coding Billing Solutions G70.00 billable status, reimbursement context
[1055]: GenHealth.ai G70.00 symptoms, diagnosis methods (antibody testing, EMG), treatment overview, related codes
[1056]: UCLA Health HCC-RAF diagnosis coding guidelines, annual recapture requirements, problem list optimization
[1057]: VYVGART billing/coding guide ICD-10-CM G70.0x usage, revenue codes
[1058]: Outsource Strategies ICD-10 codes for myasthenia gravis, G70.00 vs G70.01 distinction
[1060]: Outsource Strategies G70.00/G70.01 code usage examples
[1065]: Thymectomy surgical overview, MG treatment indications, 30% remission / 60% improvement rates
[1067]: Pyridostigmine pharmacology, dosing, mechanism for MG treatment
[1068]: HCC Institute risk adjustment factors for house calls, HCC model transition context
[1069]: Wolters Kluwer CMS-HCC V28 impact on RAF scores, model structure changes
[1071]: RAAPID CMS-HCC Model V28 full list, 115 HCC categories, 3-year transition 2024 -2026, accurate risk adjustment coding requirements
[1072]: GenHealth.ai CPT 95857 cholinesterase inhibitor challenge (Tensilon test), procedure description, MG diagnosis confirmation
[1073]: Practical Neurology thymectomy treatment options, MGTX trial results, 88% vs 54% minimal manifestation status at 5 years
[1074]: GuideWell CMS-HCC Model V28 advance notice, 3-year phased implementation blend percentages
[1075]: AAPC CPT 95857 Tensilon test coding, edrophonium injection for MG diagnosis
[1076]: Cleveland Clinic MG treatment FAQs, pyridostigmine use, thymectomy criteria, MGTX trial patient selection
[722]: HCPCS system overview (Level I = CPT, Level II = HCPCS codes for drugs/supplies)
[725]: CPT system overview, Category I/II codes
[1005]: CMS revised HCC model relative factor tables
[1059]: CMS 2023 HHS risk adjustment model coefficients

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