ICD-10 Code C84.09 – Mycosis fungoides, extranodal and solid organ sites (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C84.09 – Mycosis fungoides, extranodal and solid organ sites
What it is
C84.09 identifies mycosis fungoides involving extranodal or solid organ sites. Use it when documentation shows this cutaneous T-cell lymphoma has spread beyond the skin to a non-lymph node organ.
Clinical signs
Clinical features vary; refer to documentation. You may see records describing lymphoma involvement of an extranodal organ, confirmed by pathology, imaging, or specialist assessment.
When to use this code
Use this code when the provider documents mycosis fungoides affecting a solid organ or other extranodal site. It applies when the site is clearly identified and not limited to skin or lymph nodes.
If the note only says mycosis fungoides without site detail, do not assume this code. Check documentation for the exact involved site and whether the disease is extranodal.
Do not use for
Do not use C84.09 for skin-only mycosis fungoides or for unspecified lymphoma site. Check documentation if the record instead describes lymph node involvement or another T-cell lymphoma.
Coding tip
Code the most specific documented site, and verify that the record supports extranodal or solid organ involvement before assigning C84.09.