A81.83 maps to CMS-HCC V28 127. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · free HCC coding tools

ICD-10-CM Code View

HCC Buddy Code Card

Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupA81.83

Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Certain infectious and parasitic diseases (A00-B99) / Viral and prion infections of the central nervous system (A80-A89)

A81.83

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Fatal familial insomnia

Fatal familial insomnia is a rare inherited brain disorder that causes progressive and severe sleep disturbances, leading to deterioration of physical and mental function and ultimately death. It is caused by a genetic mutation that affects prion proteins in the brain.

Buddy Insight

Fatal familial insomnia is an extremely rare hereditary prion disease caused by a specific PRNP gene mutation (D178N with methionine at codon 129), presenting with progressive intractable insomnia, autonomic dysfunction, and eventual dementia.

Overview Risk Models Code Book Documentation Audit Notes Edition comparison

CMS-HCC V28

Mapped

HCC 127

Dementia, Mild or Unspecified

Coefficient HCC 127: 0.341 (Community Non-Dual Aged (CNA))

CMS-HCC V24

Historical

Not used for standard CY2026 Medicare Advantage payment. Select a historical period to review V24.

Not used for CY2026 payment

ACA/HHS

N/A

—

Not risk-adjusted for this model/period.

Not mapped

ESRD/PACE

Mapped

HCC 52

Dementia Without Complication

Code-level coefficient reference

RXHCC

Mapped

HCC 112

Dementia, Except Alzheimer's ...

Code-level coefficient reference

Code Book Path

Official

A81Atypical virus infections of central nervous system A81.8Other atypical virus infections of central nervous system A81.83Fatal familial insomnia

Inclusion Terms

Official

Excludes 2

Official

carrier or suspected carrier of infectious disease (Z22.-)Inherited from A00-B99
infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)Inherited from A00-B99
infectious and parasitic diseases specific to the perinatal period (P35-P39)Inherited from A00-B99
influenza and other acute respiratory infections (J00-J22)Inherited from A00-B99

Related Codes

Official

A81.81Kuru A81.82Gerstmann-Straussler-Scheinker syndrome A81.89Other atypical virus infections of central nervous system

Includes

Official

diseases generally recognized as communicable or transmissibleInherited from A00-B99, A81
diseases of the central nervous system caused by prionsInherited from A00-B99, A81

Excludes 1

Official

certain localized infections - see body system-related chaptersInherited from A00-B99, A80-A89
postpolio syndrome (G14)Inherited from A00-B99, A80-A89
sequelae of poliomyelitis (B91)Inherited from A00-B99, A80-A89
sequelae of viral encephalitis (B94.1)Inherited from A00-B99, A80-A89

Code First

Official

No Code First sequencing instructions are included in this display for A81.83. Check the code and parent instructions in the Code Book.

Use Additional

Official

code to identify resistance to antimicrobial drugs (Z16.-)Inherited from A00-B99, A81
code, if applicable, to identify:Inherited from A00-B99, A81
dementia with anxiety (F02.84, F02.A4, F02.B4, F02.C4)Inherited from A00-B99, A81
dementia with behavioral disturbance (F02.81-, F02.A1-, F02.B1-, F02.C1-)Inherited from A00-B99, A81
dementia with mood disturbance (F02.83, F02.A3, F02.B3, F02.C3)Inherited from A00-B99, A81
dementia with psychotic disturbance (F02.82, F02.A2, F02.B2, F02.C2)Inherited from A00-B99, A81
dementia without behavioral disturbance (F02.80, F02.A0, F02.B0, F02.C0)Inherited from A00-B99, A81
mild neurocognitive disorder due to known physiological condition (F06.7-)Inherited from A00-B99, A81

Code Also

Official

No Code Also instructions are included in this display for A81.83. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance

Genetic testing confirming PRNP D178N mutation with 129M haplotype

Documented family history consistent with autosomal dominant inheritance

Sleep study results showing progressive insomnia and disrupted sleep architecture

Autonomic dysfunction documentation: hypertension, tachycardia, hyperthermia, hyperhidrosis

MEAT Support

HCC Buddy guidance

Genetic testing confirming PRNP D178N mutation with 129M haplotype

Documented family history consistent with autosomal dominant inheritance

Sleep study results showing progressive insomnia and disrupted sleep architecture

Autonomic dysfunction documentation: hypertension, tachycardia, hyperthermia, hyperhidrosis

Audit Caution

HCC Buddy guidance

Coding insomnia disorder (G47.x) when the underlying cause is fatal familial insomnia — this is a prion disease, not a primary sleep disorder

Confusing FFI with sporadic fatal insomnia (which lacks the genetic mutation) — the hereditary nature is a defining feature

Not documenting the autonomic dysfunction that distinguishes FFI from other prion diseases

Failing to initiate genetic counseling documentation for at-risk family members

Common Mistakes

HCC Buddy guidance

G47.00 (Insomnia, unspecified) — Primary insomnia without the fatal prion disease component; FFI causes progressive untreatable insomnia

A81.82 (Gerstmann-Straussler-Scheinker syndrome) — Another hereditary prion disease but with cerebellar ataxia predominating rather than insomnia

A81.00 (Creutzfeldt-Jakob disease, unspecified) — CJD presents with rapid dementia; FFI has distinctive insomnia and autonomic features

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is A81.83 an HCC code?

Yes. A81.83 (Fatal familial insomnia) maps to HCC 127, Dementia, Mild or Unspecified under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.341. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.

Coder answer: A81.83 is billable and maps to V28 HCC 127, Dementia, Mild or Unspecified. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: A81.83
Description: Fatal familial insomnia
HCC (V28): HCC 127 — Dementia, Mild or Unspecified
RAF reference coefficient: 0.341
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 127, Dementia, Mild or Unspecified

0.341

ESRDHCC 52, Dementia Without Complication

Not separately weighted

RxHCCHCC 112, Dementia, Except Alzheimer's Disease

Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

Work A81.83 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for A81.83

For A81.83, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Coder workflow notes

Get the V28 mapping + MEAT cheat sheet

One printable reference: check representative V28 mappings and the documentation reminders your note needs. Free, no card.

Free PDF. No card. Unsubscribe anytime.

What This Code Means

A81.83 is the ICD-10-CM diagnosis code for fatal familial insomnia. Fatal familial insomnia is a rare inherited brain disorder that causes progressive and severe sleep disturbances, leading to deterioration of physical and mental function and ultimately death. It is caused by a genetic mutation that affects prion proteins in the brain. A81.83 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering viral and prion infections of the central nervous system (a80-a89).

Under the CMS-HCC V28 risk adjustment model, A81.83 maps to Dementia, Mild or Unspecified (HCC 127) with a source-labeled community, non-dual, aged reference coefficient of 0.341. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

This is a rare genetic disorder—verify the diagnosis is documented by a neurologist or specialist and confirm the familial/hereditary nature is established before coding. For A81.83, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, source-labeled coefficient references, and MEAT documentation criteria for A81.83 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•This is a rare genetic disorder—verify the diagnosis is documented by a neurologist or specialist and confirm the familial/hereditary nature is established before coding
•Fatal familial insomnia is reportable in many jurisdictions due to its prion disease classification; check state and facility reporting requirements and consider adding a secondary code for the genetic predisposition if applicable

Clinical Significance

Documentation Requirements

✓Genetic testing confirming PRNP D178N mutation with 129M haplotype
✓Documented family history consistent with autosomal dominant inheritance
✓Sleep study results showing progressive insomnia and disrupted sleep architecture
✓Autonomic dysfunction documentation: hypertension, tachycardia, hyperthermia, hyperhidrosis
✓Neurological progression: cognitive decline, hallucinations, motor dysfunction

Commonly Confused Codes

•G47.00 (Insomnia, unspecified): Primary insomnia without the fatal prion disease component; FFI causes progressive untreatable insomnia
•A81.82 (Gerstmann-Straussler-Scheinker syndrome): Another hereditary prion disease but with cerebellar ataxia predominating rather than insomnia
•A81.00 (Creutzfeldt-Jakob disease, unspecified): CJD presents with rapid dementia; FFI has distinctive insomnia and autonomic features