A50.42 ICD-10-CM Code: Late congenital syphilitic encephalitis
HCC Buddy Code Card
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FY 2026 Apr update / Certain infectious and parasitic diseases (A00-B99) / Infections with a predominantly sexual mode of transmission (A50-A64)
A50.42
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceLate congenital syphilitic encephalitis
This is a serious brain infection caused by syphilis that was passed from mother to child before birth and develops later in childhood or adulthood. It causes inflammation of the brain tissue and can lead to neurological problems.
CMS-HCC V28
00
RAF 0
CMS-HCC V24
00
RAF 0
ACA/HHS
00
RAF 0
ESRD/PACE
00
RAF 0
RXHCC
00
RAF 0
Code Trumping
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Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for A50.42 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for A50.42 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for A50.42 in this effective period.
Excludes 1
Official- Hutchinson's triad (A50.53)
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for A50.42 in this effective period.
Use Additional
Official- code to identify any associated mental disorder
Code Also
OfficialICD-10-CM does not list Code Also instructions for A50.42 in this effective period.
Buddy Documentation Tip
Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.
Is A50.42 an HCC code?
No. A50.42 is a billable ICD-10-CM code but does not map to any HCC category in V28, V24, ESRD, or RxHCC.
Coder workflow notes
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This code does not map to an HCC category in any model (V28, V24, ESRD, RxHCC).
What This Code Means
A50.42 is the ICD-10-CM diagnosis code for late congenital syphilitic encephalitis. This is a serious brain infection caused by syphilis that was passed from mother to child before birth and develops later in childhood or adulthood. It causes inflammation of the brain tissue and can lead to neurological problems. A50.42 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering infections with a predominantly sexual mode of transmission (a50-a64).
A50.42 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.
This code is used only for late-onset congenital syphilis (typically after age 2); ensure documentation confirms the infection was acquired congenitally and the encephalitis is a late manifestation.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for A50.42 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This code is used only for late-onset congenital syphilis (typically after age 2); ensure documentation confirms the infection was acquired congenitally and the encephalitis is a late manifestation
- •Do not use this code for early congenital syphilis or acquired syphilis; verify the patient's age and disease timeline to confirm late congenital presentation