2026 ICD-10-CM Diagnosis Code G31.9Degenerative disease of nervous system, unspecified

ICD-10-CM Codes›G00–G99›G30-G32›G31

ICD-10-CM G31.9
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

G31.9 is a billable ICD-10-CM diagnosis code for degenerative disease of nervous system, unspecified. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Neurocognitive disorders and Other nervous system disorders (often hereditary or degenerative).

Code Identity

ICD-10-CM Code
G31.9
Billable Status
Yes — Valid for Submission
Code Describes
Degenerative disease of nervous system, unspecified
Short Description
Degenerative disease of nervous system, unspecified
Same as the full description in the CMS dataset.
Parent Code
G31
Other degenerative diseases of nervous system, not elsewhere classified

Code Classification

ChapterG00–G99Diseases of the nervous system
SectionG30-G32Other degenerative diseases of the nervous system
CategoryG31Other degenerative diseases of nervous system, not elsewhere classified
This CodeG31.9Degenerative disease of nervous system, unspecified

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acquired cerebral atrophy
  • Atrophy of brainstem
  • Atrophy of caudate nucleus
  • Atrophy of cerebellar vermis
  • Atrophy of cortex of frontal and temporal lobe
  • Atrophy of cortex of frontal lobe
  • Atrophy of cortex of occipital lobe
  • Atrophy of cortex of parietal lobe
  • Atrophy of cortex of temporal lobe
  • Atrophy of hilum of dentate nucleus
  • Atrophy of hippocampus
  • Atrophy of hypothalamus
  • Atrophy of inner granular layer of cerebellar cortex
  • Atrophy of pons and cerebellum
  • Atrophy of Purkinje cells of cerebellar cortex
  • Atrophy of pyramidal tract
  • Atrophy of spinocerebellar tract
  • Autonomic nervous system disorder co-occurrent and due to neurodegenerative disorder
  • Cerebellar degeneration
  • Cerebral atrophy
  • Cerebral degeneration
  • Cerebral degeneration due to Creutzfeldt-Jakob disease
  • Cerebral degeneration due to Parkinson's disease
  • Cerebral degeneration presenting primarily with dementia
  • Chorea due to heredodegenerative disorder
  • Chronic deafness
  • Circumscribed atrophy of brain
  • Congenital blindness
  • Degenerative brain disorder
  • Degenerative disease of the central nervous system
  • Diffuse atrophy of cerebellum
  • Diffuse atrophy of cerebrum
  • Epilepsy co-occurrent and due to degenerative brain disorder
  • Fibrosis, neurodegeneration, cerebral angiomatosis syndrome
  • Frontal lobe degeneration
  • Frontal lobe degeneration with motor neurone disease
  • Frontotemporal degeneration
  • Gemignani syndrome
  • Global brain atrophy
  • Hemiatrophy of cerebellar cortex
  • Hemiatrophy of cerebral cortex
  • Hydrocephalus ex vacuo
  • Hydrocephalus ex vacuo due to degenerative brain disorder
  • Microphthalmia with brain atrophy syndrome
  • Parkinsonian pyramidal syndrome
  • Parkinsonism due to heredodegenerative disorder
  • PF-ILD-progressive fibrosing interstitial lung disease
  • Posterior cortical atrophy syndrome
  • Prieto Badia Mulas syndrome
  • Progressive focal cortical atrophy
  • Secondary cerebellar degeneration

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Atrophy, atrophic(of)
      • brain (cortex) (progressive)
    • Degeneration, degenerative
      • brain (cortical) (progressive)
    • Degeneration, degenerative
      • brain (cortical) (progressive)
        • childhood
    • Degeneration, degenerative
      • cerebellar NOS
    • Degeneration, degenerative
      • nervous system
    • Hemiatrophy
      • cerebellar

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NVS011
Neurocognitive disorders
Default principal diagnosis: inpatient Yes · outpatient Yes
CCSR NVS006
Other nervous system disorders (often hereditary or degenerative)
Default principal diagnosis: inpatient No · outpatient No

Clinical InformationClinical

  • CDR1 Gene|CDR1|CDR1|Cerebellar Degeneration-Related Protein-1 (34kD) Gene

    this gene plays a major role in antigens that are specifically expressed in neuronal cells.

  • CDR1 wt Allele|CDR|CDR Gene|CDR1|CDR34|CDR34 Gene|CDR62A|CDR62A Gene|Cerebellar Degeneration-Related Autoantigen 1 Gene|Cerebellar Degeneration-Related Protein (34kD) Gene|Cerebellar Degeneration-Related Protein-1 (34kD) wt Allele|Cerebellar-Degeneration-Related Antigen 1 Gene

    human cdr1 wild-type allele is located within xq27.1-q27.2 and is approximately 1 kb in length. this allele, which encodes cerebellar degeneration-related antigen 1 protein, is involved in immune reactions and neuronal antigen regulation.

  • Cerebellar Degeneration

    degeneration of the cerebellum. it may be an inherited condition, a paraneoplastic syndrome, or secondary to autoimmune disorders.

  • Cerebellar-Degeneration-Related Antigen 1|CDR|CDR1|CDR1 Protein|CDR34|CDR62A|Cerebellar Degeneration-Related Autoantigen 1|Cerebellar Degeneration-Related Autoantigen, 34-kD|Cerebellar Degeneration-Related Protein (34kD)|Cerebellar Degeneration-Related Protein 1|Cerebellar Degeneration-Related Protein 1, 34kDa|Cerebellar Degeneration-Related Protein-1 (34kD)

    cerebellar degeneration-related antigen 1 (262 aa, ~31 kda) is encoded by the human cdr1 gene. this protein is involved in autoimmune diseases.

  • Paraneoplastic Cerebellar Degeneration

    a rare, immune-mediated disorder characterized by cerebellar degeneration due to the presence of an often undetected malignancy (usually carcinoma or lymphoma) in an anatomic site other than the cerebellum. signs and symptoms include progressive ataxia, dysarthria, and nystagmus.

  • Spinocerebellar Ataxia|Spinocerebellar Degeneration

    an inherited disorder characterized by degeneration of the spinal cord and the cerebellum. symptoms may appear at any age and include progressive loss of coordination of gait, hands, speech, and eye movements.

  • CDR1 Gene|CDR1|CDR1|Cerebellar Degeneration Related 1 Gene

    this gene plays a major role in antigens that are specifically expressed in neuronal cells.

  • CDR1 wt Allele|CDR|CDR34|CDR62A|Cerebellar Degeneration Related 1 wt Allele|Cerebellar Degeneration-Related Autoantigen 1 Gene|Cerebellar Degeneration-Related Autoantigen, 34-kD Gene|Cerebellar Degeneration-Related Protein (34kD) Gene|Cerebellar Degeneration-Related Protein-1 (34kD) Gene|Cerebellar-Degeneration-Related Antigen 1 Gene

    human cdr1 wild-type allele is located within xq27.1-q27.2 and is approximately 1 kb in length. this allele, which encodes cerebellar degeneration-related antigen 1 protein, is involved in immune reactions and neuronal antigen regulation.

  • Cerebellar Degeneration-Related Antigen 1|CDR|CDR1|CDR1 Protein|CDR34|CDR62A|Cerebellar Degeneration-Related Autoantigen 1|Cerebellar Degeneration-Related Autoantigen, 34-kD|Cerebellar Degeneration-Related Protein (34kD)|Cerebellar Degeneration-Related Protein 1, 34kDa|Cerebellar Degeneration-Related Protein-1 (34kD)|Cerebellar-Degeneration-Related Antigen 1

    cerebellar degeneration-related antigen 1 (262 aa, ~31 kda) is encoded by the human cdr1 gene. this protein is involved in autoimmune diseases.

Patient EducationClinical

Degenerative Nerve Diseases

Degenerative nerve diseases affect many of your body's activities, such as balance, movement, talking, breathing, and heart function. Many of these diseases are genetic. Sometimes the cause is a medical condition such as alcoholism, a tumor, or a stroke. Other causes may include toxins, chemicals, and viruses.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert G31.9 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
330.9 Cereb degen in child NOS
Approximate The match is approximate rather than exact.
ICD-9-CM
331.9 Cereb degeneration NOS
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About G31.9Overview

Is G31.9 a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report degenerative disease of nervous system, unspecified on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What is the ICD-9 equivalent of G31.9?

Under the General Equivalence Mappings, degenerative disease of nervous system, unspecified converts to ICD-9-CM 330.9 (cereb degen in child NOS) and 331.9 (cereb degeneration NOS). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.