2026 ICD-10-CM Diagnosis Code A50.42Late congenital syphilitic encephalitis

ICD-10-CM Codes›A00–B99›A50-A64›A50

ICD-10-CM A50.42
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

A50.42 is a billable ICD-10-CM diagnosis code for late congenital syphilitic encephalitis. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). Coders also document this condition as congenital syphilitic encephalitis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Encephalitis, Perinatal infections, and Sexually transmitted infections (excluding HIV and hepatitis).

Code Identity

ICD-10-CM Code
A50.42
Billable Status
Yes — Valid for Submission
Code Describes
Late congenital syphilitic encephalitis
Short Description
Late congenital syphilitic encephalitis
Same as the full description in the CMS dataset.
Parent Code
A50.4
Late congenital neurosyphilis [juvenile neurosyphilis]

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA50-A64Infections with a predominantly sexual mode of transmission
CategoryA50Congenital syphilis
This CodeA50.42Late congenital syphilitic encephalitis

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Congenital syphilitic encephalitis
  • Late congenital neurosyphilis
  • Late congenital syphilis
  • Syphilitic encephalitis

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.

    • Encephalitis(chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
      • in (due to)
        • syphilis
          • congenital

Clinical ClassificationClinical

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

CCSR NVS002
Encephalitis
Default principal diagnosis: inpatient No · outpatient No
CCSR PNL009
Perinatal infections
Default principal diagnosis: inpatient Yes · outpatient Yes
CCSR INF010
Sexually transmitted infections (excluding HIV and hepatitis)
Default principal diagnosis: inpatient No · outpatient No

Patient EducationClinical

Encephalitis

Encephalitis is inflammation (swelling) of the brain. It can happen when an infection or medical condition that affects the brain activates your immune system. The inflammation can cause a wide range of symptoms. In extreme cases, it can lead to brain damage, stroke, or even death.

The full article covers:

  • What is encephalitis?
  • What causes encephalitis?
  • Who is more likely to get encephalitis?
  • What are the symptoms of encephalitis?
  • How is encephalitis diagnosed?
  • What are the treatments for encephalitis?
  • Can encephalitis be prevented?

Read the full article at MedlinePlus

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

Convert A50.42 to ICD-9-CMHistory

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

ICD-9-CM
090.41 Congen syph encephalitis
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 A50.42Overview

Is A50.42 (Late congenital neurosyphilis [juvenile neurosyphilis]) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report late congenital syphilitic encephalitis on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What is the ICD-9 equivalent of A50.42?

Under the General Equivalence Mappings, late congenital syphilitic encephalitis converts to ICD-9-CM 090.41 (congen syph encephalitis). 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.