C84.01
BillableMycosis fungoides, lymph nodes of head, face, and neck
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C84.01 an HCC code?
Yes. C84.01 maps to Lung and Other Severe Cancers under the CMS-HCC V28 risk adjustment model (and Lymphoma and Other Cancers under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
MEAT Criteria for C84.01
For C84.01 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically — it has to be re-documented and supported each calendar year.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed C84.01 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C84.01 is the ICD-10-CM diagnosis code for mycosis fungoides, lymph nodes of head, face, and neck. A rare type of skin cancer (mycosis fungoides) that has spread to the lymph nodes in the head, face, and neck area. C84.01 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of lymphoid, hematopoietic and related tissue (c81-c96).
Under the CMS-HCC V28 risk adjustment model, C84.01 maps to Lung and Other Severe Cancers (HCC 20) with a community, non-dual, aged base RAF weight of 0.000. Under the older CMS-HCC V24 model, C84.01 maps to Lymphoma and Other Cancers (HCC 10) with a community, non-dual, aged base RAF weight of 0.675. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
Verify lymph node involvement in the head/neck region through imaging or biopsy. Because C84.01 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for C84.01 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify lymph node involvement in the head/neck region through imaging or biopsy
- •The '1' designator specifically indicates cervical and head/neck lymph node sites
Clinical Significance
Mycosis fungoides with involvement of head, face, and neck lymph nodes indicates progression beyond purely cutaneous disease. Lymph node involvement in mycosis fungoides represents a higher stage (Stage III-IV) and typically signals the need for systemic therapy rather than skin-directed treatment alone. This progression carries worse prognosis than skin-limited disease.
Documentation Requirements
- ✓Skin biopsy confirming mycosis fungoides
- ✓Lymph node biopsy or imaging confirming head/face/neck lymph node involvement
- ✓Distinction between reactive lymphadenopathy (common in mycosis fungoides) and pathologically confirmed lymph node involvement
- ✓TNMB staging reflecting nodal involvement
- ✓Current treatment plan addressing both cutaneous and nodal disease
Commonly Confused Codes
- •C84.00 — Mycosis fungoides, unspecified site: Use C84.01 when head/face/neck lymph node involvement is confirmed pathologically
- •C84.11 — Sezary disease, head/face/neck: Sezary disease is distinct from mycosis fungoides despite both being cutaneous T-cell lymphomas
- •C83.91 — Non-follicular lymphoma, unspecified, head/face/neck: Use when the lymphoma type is non-follicular but not mycosis fungoides