ICD-10 Code A51.3 – Secondary syphilis of skin and mucous membranes (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code A51.3 – Secondary syphilis of skin and mucous membranes
What it is
A51.3 identifies secondary syphilis with involvement of the skin and mucous membranes. Use it when the infection has entered the secondary stage and the documented findings include mucocutaneous lesions.
Clinical signs
Findings often include a generalized rash, mucous patches, or condyloma lata. Clinical features vary; refer to documentation, especially when the record does not clearly describe skin or mucous membrane involvement.
When to use this code
Use this code when the provider documents secondary syphilis and specifically notes lesions on the skin, oral mucosa, genital mucosa, or other mucous membranes. It also fits when the diagnosis is confirmed in the assessment and the anatomic involvement is stated clearly.
If the chart only says syphilis, or if the stage is not identified, check documentation before coding. Do not assume mucocutaneous involvement without provider support.
Do not use for
Do not use A51.3 for primary syphilis, latent syphilis, or tertiary disease. Avoid this code when skin findings are unrelated to syphilis or when the record does not support secondary-stage infection.
Coding tip
Confirm both the stage and the mucocutaneous involvement in the provider note before assigning A51.3.