🧬 ICD-10 CM G36.1 — Acute and Subacute Hemorrhagic Leukoencephalitis [Hurst]
Billable Code Confirmed
ICD-10 CM G36.1 is a fully specified, 4-character billable code requiring no further laterality, episode, or manifestation digit. It sits directly beneath the non-billable header G36 and can be reported as a stand-alone principal or secondary diagnosis on any claim type.
Non-Billable Parent Codes
G36 (Other acute disseminated demyelination) is a non-billable category header — it exists only to organize G36.0-G36.9 and cannot itself be submitted on a claim; the coder must always drop down to the fourth character.
Clinical Context
Hurst disease is distinguished from typical postinfectious ADEM by its hyperacute, often fulminant course and pathologic hemorrhagic necrosis of cerebral white matter, which drives the sequencing away from **G04.01**¹ and toward G36.1 whenever the provider documents the hemorrhagic/necrotizing variant.
Code Classification
ICD-10 CM G36.1 is a diagnosis code only — it carries no procedural, DRG-grouping-independent weight of its own and must always be paired with supporting CPT/HCPCS and, for inpatient PCS purposes, applicable procedure codes to reflect the workup and treatment rendered.
🔍 Code Description
Acute and subacute hemorrhagic leukoencephalitis, widely known as Hurst disease or Weston Hurst syndrome, is a rare and severe fulminant variant of acute disseminated encephalomyelitis characterized by rapid-onset perivascular hemorrhage and necrosis of cerebral white matter.² It most often follows a preceding viral illness or, less commonly, vaccination, and presents with abrupt encephalopathy, fever, seizures, and focal neurologic deficits that can progress to coma within days. Because of its explosive course and high mortality without aggressive treatment, it is treated as a neurological emergency requiring ICU-level care, high-dose corticosteroids, and often escalation to 96365 infusion-based immunotherapy or 36514 therapeutic apheresis when steroid response is inadequate.
Diagnosis relies on a combination of clinical presentation and neuroimaging, typically 70553 MRI brain, which demonstrates asymmetric hemorrhagic white-matter lesions with surrounding edema, sometimes supplemented by 62270 diagnostic lumbar puncture to evaluate cerebrospinal fluid pleocytosis and rule out infectious or malignant etiologies. Documentation specifying “hemorrhagic,” “necrotizing,” or “Hurst” is essential to support G36.1 rather than the more common, non-hemorrhagic postinfectious ADEM code G04.01, since the two conditions are mutually exclusive under the Excludes1 note and represent clinically distinct entities despite overlapping presentations.
🌳 Code Tree / Hierarchy
G36 Other acute disseminated demyelination ❌ Non-billable
│
├── G36.0 Neuromyelitis optica [Devic] ✅ Billable
├── G36.1 Acute and subacute hemorrhagic leukoencephalitis [Hurst] ◀ THIS CODE ✅ Billable
├── G36.8 Other specified acute disseminated demyelination ✅ Billable
└── G36.9 Acute disseminated demyelination, unspecified ✅ BillableHemorrhagic vs. Postinfectious Distinction
Tip
✅ Includes
- Hurst disease — the eponymous term most frequently used interchangeably with the formal code title in clinical documentation.
- Acute necrotizing hemorrhagic leukoencephalopathy — pathology-driven terminology describing the destructive white-matter process captured by this code.
- Weston Hurst syndrome — historical eponym referencing the original 1941 case description; still appears in neurology and neuropathology notes.
❌ Excludes
Excludes 1
- G04.01 — Postinfectious ADEM: mutually exclusive with G36.1 because Hurst disease is defined by its hemorrhagic/necrotizing pathology, whereas G04.01 describes the non-hemorrhagic postinfectious form; only one may be coded per encounter based on documented pathology.
Danger
Excludes 2
- A00-B99 (certain infectious and parasitic diseases) — the antecedent infection that triggered the hemorrhagic leukoencephalitis may be coded separately when clinically significant and actively treated.
- R00-R94 (symptoms, signs and abnormal clinical findings) — acute symptoms such as seizure or altered mental status may be separately reportable when not integral to the underlying disease process per inpatient coding guidelines.
📋 Clinical Overview
Hurst Disease vs. Related Demyelinating Presentations
Because G36.1 sits in a DRG family shared with several other acute and chronic demyelinating diagnoses, distinguishing documentation is critical for both clinical accuracy and correct reimbursement.
| Feature | G36.1 | Related G04.01 | Related G36.9 |
|---|---|---|---|
| Pathology | Hemorrhagic, necrotizing white-matter destruction | Non-hemorrhagic perivenous demyelination | Nonspecific/undetermined acute demyelination |
| Course | Fulminant, often days to coma | Subacute, days to weeks | Variable, insufficiently documented |
| Typical trigger | Preceding viral infection | Preceding infection or vaccination | Not specified in documentation |
Important
A CDI trigger should fire whenever a note documents “hemorrhagic” or “necrotizing” white-matter disease coded only as unspecified ADEM — this is a common under-specification that understates severity for DRG and HCC purposes.
Manifestations & Symptom Burden
- Encephalopathy — altered mental status ranging from confusion to coma is nearly universal and often the presenting complaint.
- Seizures — new-onset seizure activity is common and may require separate reporting when clinically significant.
- Focal neurologic deficits — hemiparesis, cranial nerve palsies, and aphasia reflect the location of hemorrhagic lesions.
- Signs of increased intracranial pressure — papilledema, vomiting, and declining consciousness signal a medical emergency requiring ICU management.
Tip
Manifestations that are integral to the disease process (encephalopathy, seizure secondary to the demyelination) are generally not coded separately unless they meet reportable-complication criteria per inpatient coding guidelines — verify against the specific payer’s guidance.
💰 HCC Risk Adjustment
ICD-10 CM G36.1 maps to the Multiple Sclerosis HCC category (V28 HCC 198; V24 HCC 77) alongside its sibling demyelinating codes.³ Because the underlying RAF weight and phase-in percentage change annually and are not contained in the project’s local files, the exact dollar/weight contribution must be independently verified against the current CMS-HCC V28 risk adjustment model file before use in any risk score calculation. MEAT documentation (Monitor, Evaluate, Assess, or Treat) must be present at the specific encounter — a diagnosis simply carried forward on a problem list without active management does not support HCC capture for that date of service.
🏥 MS-DRG Assignment
ICD-10 CM G36.1, when reported as principal diagnosis, groups to MDC 01 (Diseases and Disorders of the Nervous System), DRG 058-060 “Multiple Sclerosis and Cerebellar Ataxia,” alongside multiple sclerosis and hereditary ataxia codes.⁴ Assignment among DRG 058 (with MCC), 059 (with CC), and 060 (without CC/MCC) is driven entirely by secondary diagnosis severity — commonly respiratory failure, sepsis, or acute encephalopathy pushing the case to the MCC tier. There is no disease-specific NCD directly covering the G36.1 diagnosis itself; however, if therapeutic apheresis (36514) is performed, NCD 110.14 (Apheresis/Therapeutic Pheresis) does not explicitly list ADEM/Hurst disease among its enumerated covered indications, so medical necessity documentation supporting apheresis for this diagnosis should be reviewed against the current NCD/MAC LCD language before claim submission — flagged for independent verification.
🔗 Related ICD-10-CM Codes
Demyelinating/CNS inflammatory group:
- G36.0 — Neuromyelitis optica [Devic]
- G36.8 — Other specified acute disseminated demyelination
- G36.9 — Acute disseminated demyelination, unspecified
- G04.01 — Postinfectious ADEM (Excludes1 pair)
- G04.90 — Encephalitis and encephalomyelitis, unspecified
Associated symptom/complication group:
- R56.9 — Unspecified convulsions
- G93.89 — Other specified disorders of brain
- R40.2011 — Unspecified coma, Glasgow coma scale score 13-15
🛠️ Commonly Associated CPT Codes
- 70553 — MRI brain without and with contrast; the primary imaging study confirming hemorrhagic demyelinating lesions and monitoring treatment response.
- 62270 — Diagnostic lumbar puncture; performed to obtain CSF for inflammatory marker and infectious workup, and to exclude alternate diagnoses.
- 96365 — Therapeutic, prophylactic, or diagnostic IV infusion, initial hour; used for high-dose steroid or IVIG administration.
- 36514 — Therapeutic apheresis for plasma exchange; escalation therapy when steroid/IVIG response is inadequate.
- 99291 — Critical care, first hour; frequently reportable given the ICU-level acuity of this diagnosis.
🏷️ Modifier Reference
| Modifier | Name | When to Apply |
|---|---|---|
| -25 | Significant, Separately Identifiable E/M | Append when a significant E/M service (e.g., initial neurology consult) is performed the same day as a procedure such as 62270. |
| -59 | Distinct Procedural Service | Use when 62270 or 36514 is performed as a distinct service not otherwise bundled with another same-day procedure. |
| -52 | Reduced Services | Apply if a planned apheresis or infusion session is terminated early for a clinical reason without full completion of the intended service. |
| -53 | Discontinued Procedure | Use when a procedure such as lumbar puncture is started but discontinued due to patient instability before completion. |
| -76 | Repeat Procedure by Same Physician | Applies to repeat 36514 apheresis sessions or repeat 70553 imaging performed by the same provider during the stay. |
| -77 | Repeat Procedure by Another Physician | Applies when a repeat imaging or apheresis session is performed by a different provider than the one who performed the initial service. |
NCCI Bundling Considerations
CPT 96365 infusion administration is frequently bundled with other same-day infusion or injection codes under NCCI edits and requires modifier -59 or an appropriate X{EPSU} modifier to unbundle when clinically distinct; 62270 may bundle with fluoroscopic guidance codes if imaging guidance is billed separately without meeting distinct medical necessity documentation.
🔬 ICD-10-PCS Crosswalk
Note: The following PCS codes are not sourced from a project PCS reference file and must be independently verified character-by-character before inpatient claim submission.
- 6A550Z3 — Pheresis of physiological systems, circulatory, single — represents the inpatient procedural equivalent of therapeutic apheresis when performed during an admission for G36.1.
- 009U3ZX — Drainage of spinal canal, percutaneous approach, diagnostic — captures the inpatient PCS equivalent of a diagnostic lumbar puncture performed to work up this diagnosis.
- 3E0G3GC — Introduction of other therapeutic substance into central nervous system, percutaneous approach — potentially applicable for high-dose steroid or immunomodulator administration depending on route documented; character selection requires chart-specific verification.
💊 Coding Scenarios and Examples
Example 1
Clinical Scenario: A previously healthy adult presents 10 days after a viral upper respiratory illness with rapidly progressive encephalopathy and hemiparesis. MRI brain shows asymmetric hemorrhagic white-matter lesions consistent with Hurst disease. The patient is admitted to the ICU and started on high-dose IV steroids.
| Field | Code | Rationale |
|---|---|---|
| CPT | 70553 | MRI brain w/wo contrast confirming hemorrhagic demyelinating lesions. |
| CPT 2 | 96365 | Initial hour of IV steroid infusion administration. |
| PDx | G36.1 | Documented hemorrhagic pathology on imaging supports Hurst disease over unspecified ADEM. |
Tip
Sequencing G36.1 as principal diagnosis groups the case to DRG 058-060; secondary diagnosis of encephalopathy should be evaluated for MCC/CC impact based on documented severity.
Example 2
Clinical Scenario: A patient with confirmed G36.1 fails to improve after 5 days of steroid therapy. The neurology team initiates therapeutic plasma exchange, and a diagnostic lumbar puncture is performed the same admission to exclude an infectious process.
| Field | Code | Rationale |
|---|---|---|
| CPT | 36514 | Therapeutic apheresis for plasma exchange as steroid-refractory escalation therapy. |
| CPT 2 | 62270--59 | Diagnostic lumbar puncture reported as a distinct service from the apheresis session. |
| PDx | G36.1 | Principal diagnosis remains Hurst disease throughout the admission. |
Tip
Verify apheresis medical necessity documentation against current NCD 110.14 and applicable MAC LCD language, since ADEM/Hurst disease is not explicitly enumerated as a covered indication.
Example 3
Clinical Scenario: An inpatient with G36.1 develops acute respiratory failure requiring mechanical ventilation during the ICU stay, in addition to ongoing critical care management.
| Field | Code | Rationale |
|---|---|---|
| CPT | 99291 | Critical care, first hour, for ongoing intensive management of the acute neurologic emergency. |
| PDx | G36.1 | Principal diagnosis driving the admission and DRG assignment. |
Tip
Documented acute respiratory failure as a secondary diagnosis will push DRG assignment to 058 (with MCC) rather than 059 or 060 — confirm the secondary diagnosis is fully supported in the record before finalizing DRG assignment.
⚠️ Coding Pitfalls and Tips
- Pitfall 1: Confusing G36.1 (Hurst disease) with the similarly-spelled but clinically unrelated E76.01 (Hurler’s syndrome, a mucopolysaccharidosis); the names sound alike but the conditions and code chapters are entirely different. Tips: Always confirm the diagnosis is a demyelinating CNS condition, not a metabolic storage disorder, before code selection.
- Pitfall 2: Reporting the non-billable parent G36 directly on a claim. Tips: Always drop to the fourth character (G36.0-G36.9) based on documented specificity.
- Pitfall 3: Coding both G36.1 and G04.01 for the same encounter despite the Excludes1 edit. Tips: Query the provider when documentation uses “ADEM” and “hemorrhagic/Hurst” interchangeably to clarify the specific entity being treated.
- Pitfall 4: Defaulting to G36.9 (unspecified) when the chart clearly documents hemorrhagic or necrotizing features. Tips: Abstract the pathology/imaging findings carefully — “hemorrhagic” or “Hurst” in the note supports the more specific G36.1.
- Pitfall 5: Assuming apheresis (36514) is automatically covered under NCD 110.14 for this diagnosis. Tips: Confirm medical necessity documentation independently, since Hurst disease/ADEM is not among the NCD’s enumerated covered indications.
- Pitfall 6: Carrying G36.1 forward on a problem list for HCC capture without current-encounter MEAT documentation. Tips: Re-document monitoring, evaluation, assessment, or treatment of the condition at each qualifying encounter to support risk adjustment.
📚 Sources
1. Centers for Medicare & Medicaid Services. *ICD-10-CM Official Guidelines for Coding and Reporting, FY2026.* CMS/NCHS; 2026. 2. AAPC. *ICD-10-CM Code G36.1 — Acute and Subacute Hemorrhagic Leukoencephalitis [Hurst].* AAPC Codify; 2026. https://www.aapc.com/codes/icd-10-codes/G36.1 3. HCCBuddy. *G36.1 HCC Category Mapping (CMS-HCC V28/V24).* 2026. https://hccbuddy.com/icd10/G36.1 4. Centers for Medicare & Medicaid Services. *ICD-10-CM/PCS MS-DRG v43.0/v44.0 Definitions Manual — MDC 01, DRG 058-060.* CMS; 2026. https://www.cms.gov/icd10m 5. Centers for Medicare & Medicaid Services. *National Coverage Determination 110.14 — Apheresis (Therapeutic Pheresis).* CMS Medicare Coverage Database; 2026. https://www.cms.gov/medicare-coverage-databaseSources listed above correspond to superscript citations throughout this note. Verify all Medicare payment figures against your current CMS PFS Lookup tool and applicable MAC LCD prior to claim submission. Please use the latest AAPC/AHIMA Coding Books to verify each code within this note.