2026 ICD-10-CM Diagnosis Code R94.01Abnormal electroencephalogram [EEG]

ICD-10-CM Codes›R00–R99›R90-R94›R94

ICD-10-CM R94.01
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

R94.01 is a billable ICD-10-CM diagnosis code for abnormal electroencephalogram [EEG]. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). As a symptom code, it should not be used as a principal diagnosis once a related definitive diagnosis has been established. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Abnormal findings without diagnosis.

Code Identity

ICD-10-CM Code
R94.01
Billable Status
Yes — Valid for Submission
Code Describes
Abnormal electroencephalogram [EEG]
Short Description
Abnormal electroencephalogram [EEG]
Same as the full description in the CMS dataset.
Parent Code
R94.0
Abnormal results of function studies of central nervous system

Code Classification

ChapterR00–R99Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified
SectionR90-R94Abnormal findings on diagnostic imaging and in function studies, without diagnosis
CategoryR94Abnormal results of function studies
This CodeR94.01Abnormal electroencephalogram [EEG]

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Alpha amplitude asymmetry
  • Alpha coma type recording
  • Alpha frequency asymmetry
  • Asymmetric beta activity
  • Asymmetric EEG
  • Asymmetrical mu activity
  • Beta coma type recording
  • Bilateral periodic epileptiform discharges
  • Burst suppression
  • Café-au-lait macules with temporal dysrhythmia
  • Continuous periodic complexes
  • Dominant alpha activity
  • Dominant beta activity
  • Dominant delta activity
  • Dominant EEG frequency - finding
  • Dominant theta activity
  • EEG abnormality with seizure
  • EEG abnormality without seizure
  • EEG artifact
  • EEG artifact - patient movement
  • EEG artifact - technical problems
  • EEG pattern of uncertain significance
  • EEG symmetry - finding
  • Electrocerebral silence
  • Electroencephalogram abnormal
  • Excessive overbreathing response
  • Focal continuous delta activity
  • Focal continuous EEG abnormality
  • Focal continuous theta activity
  • Focal episodic delta activity
  • Focal episodic EEG abnormality
  • Focal episodic sharp waves
  • Focal episodic spike wave
  • Focal episodic spike wave with secondary generalization
  • Focal episodic spikes
  • Focal episodic theta activity
  • Focal recruiting discharge
  • Focal reduction of EEG activity
  • Focal rolandic spikes
  • Focal sharp waves
  • Focal spikes
  • Frontal intermittent rhythmic delta activity
  • Generalized atypical spike wave
  • Generalized continuous EEG abnormality
  • Generalized EEG amplitude asymmetry
  • Generalized EEG frequency asymmetry
  • Generalized EEG pattern - finding
  • Generalized epileptiform discharges
  • Generalized episodic EEG abnormality
  • Generalized intermittent delta activity
  • Generalized intermittent theta activity
  • Generalized multifocal spikes
  • Generalized slow spike wave
  • Generalized three per second spike wave
  • Intermittent periodic complexes
  • Isoelectric recording
  • Light-induced EEG abnormality
  • Loss of reactivity
  • Low amplitude EEG tracing
  • Low amplitude six per second spike wave
  • Low frequency alpha activity
  • Low frequency background activity
  • Low frequency delta activity
  • Low frequency theta activity
  • Occipital intermittent rhythmic delta activity
  • Periodic complexes
  • Periodic lateralized epileptiform discharges
  • Positive spikes
  • Prolonged overbreathing response
  • Reduction of alpha activity in left cerebral hemisphere
  • Reduction of alpha activity in right cerebral hemisphere
  • Rhythmic mid-temporal discharge
  • Small sharp transients during sleep
  • Sound-induced EEG abnormality
  • Subclinical rhythmical EEG discharges in adults
  • Temporal slowing
  • Trace alternant EEG pattern
  • Triphasic waves

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.

    • Abnormal, abnormality, abnormalities
      • electroencephalogram [EEG]

Clinical ClassificationClinical

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

CCSR SYM017
Abnormal findings without diagnosis
Default principal diagnosis: inpatient Yes · outpatient Yes

Convert R94.01 to ICD-9-CMHistory

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

ICD-9-CM
794.02 Abn electroencephalogram
Exact Match The mapping is direct, with no qualifiers.

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 R94.01Overview

Is R94.01 a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report abnormal electroencephalogram [EEG] on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

Can R94.01 be a principal diagnosis?

Use it with care. This is a symptom code, so once a definitive diagnosis explaining the abnormal electroencephalogram [EEG] is established, that condition takes the principal position instead.

What is the ICD-9 equivalent of R94.01?

Under the General Equivalence Mappings, abnormal electroencephalogram [EEG] converts to ICD-9-CM 794.02 (abn electroencephalogram). The mapping is a direct match.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.