2027 ICD-10-CM Diagnosis Code G99.8Other specified disorders of nervous system in diseases classified elsewhere

ICD-10-CM Codes›G00–G99›G89-G99›G99

ICD-10-CM G99.8
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

G99.8 is a billable ICD-10-CM diagnosis code for other specified disorders of nervous system in diseases classified elsewhere. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 70 through 72. The code is a manifestation code that cannot be reported as the principal diagnosis. Coders also document this condition as epilepsy syndrome with progressive neurological deterioration. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other nervous system disorders (neither hereditary nor degenerative).

Code Identity

ICD-10-CM Code
G99.8
Billable Status
Yes — Valid for Submission
Code Describes
Other specified disorders of nervous system in diseases classified elsewhere
Short Description
Oth disrd of nervous system in diseases classified elsewhere
Parent Code
G99
Other disorders of nervous system in diseases classified elsewhere

Code Classification

ChapterG00–G99Diseases of the nervous system
SectionG89-G99Other disorders of the nervous system
CategoryG99Other disorders of nervous system in diseases classified elsewhere
This CodeG99.8Other specified disorders of nervous system in diseases classified elsewhere

Code EditsBilling

Medicare Code Editor checks that affect claim validity for G99.8.

Manifestation diagnoses
Manifestation codes describe the manifestation of an underlying disease, not the disease itself, and therefore should not be used as a principal diagnosis.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Epilepsy syndrome with progressive neurological deterioration
  • Neurologic disorder due to degeneration of lumbar intervertebral disc
  • Neuroschistosomiasis
  • Peripheral neuropathy due to metabolic disorder

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to G99.8: its own notes plus those printed at Chapter 6. A note printed at a category, block or chapter applies to every code under it.

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 6 (G00-G99) Diseases of the nervous system applies to 700 codes
  • certain conditions originating in the perinatal period (P04-P96)
  • certain infectious and parasitic diseases (A00-B99)
  • complications of pregnancy, childbirth and the puerperium (O00-O9A)
  • congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
  • endocrine, nutritional and metabolic diseases (E00-E88)
  • injury, poisoning and certain other consequences of external causes (S00-T88)
  • neoplasms (C00-D49)
  • symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)

Code First

The underlying condition named in the note is sequenced before this code.

  • underlying disorder, such as:
  • amyloidosis (E85.-)
  • avitaminosis (E56.-)

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Clinical ClassificationClinical

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

CCSR NVS020
Other nervous system disorders (neither hereditary nor degenerative)
Default principal diagnosis: inpatient No · outpatient No

Patient EducationClinical

Neurologic Diseases

The brain, spinal cord, and nerves make up the nervous system. Together they control all the workings of the body. When something goes wrong with a part of your nervous system, you can have trouble moving, speaking, swallowing, breathing, or learning. You can also have problems with your memory, senses, or mood.

Read the full article at MedlinePlus

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

Convert G99.8 to ICD-9-CMHistory

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

ICD-9-CM
349.89 Cns disorder NEC
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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About G99.8Overview

Is G99.8 a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report other specified disorders of nervous system in diseases classified elsewhere on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does G99.8 group to?

On inpatient claims, other specified disorders of nervous system in diseases classified elsewhere maps to MS-DRG 72, 70, 71, with relative weights from 0.7344 to 1.6089 depending on complications. Higher weights mean higher Medicare reimbursement.

Can G99.8 be a principal diagnosis?

No. This is a manifestation code: other specified disorders of nervous system in diseases classified elsewhere describes the manifestation of an underlying disease rather than the disease itself, so the underlying condition is sequenced first.

Can G99.8 be reported with B69.0?

Not as a rule. The Excludes1 note on G99.8 lists "cysticercosis (B69.0)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).

What is coded first with G99.8?

The Code First note reads: underlying disorder, such as: amyloidosis (E85.-); avitaminosis (E56.-). When one of these applies, it is sequenced before G99.8.