C84.18
BillableSézary disease, lymph nodes of multiple sites
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C84.18 an HCC code?
Yes. C84.18 maps to Metastatic Cancer and Acute Leukemia 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 C84.18
For C84.18 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 C84.18 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C84.18 is the ICD-10-CM diagnosis code for sézary disease, lymph nodes of multiple sites. Sézary disease is a rare type of blood cancer that affects T-cells (a type of white blood cell) and causes skin problems, itching, and enlarged lymph nodes in multiple areas of the body. This code specifically indicates the disease has spread to lymph nodes in more than one location. C84.18 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, C84.18 maps to Metastatic Cancer and Acute Leukemia (HCC 17) with a community, non-dual, aged base RAF weight of 0.368. Under the older CMS-HCC V24 model, C84.18 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 documentation specifies involvement of multiple lymph node sites; if only one site is involved, use C84.10 instead. Because C84.18 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 C84.18 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify documentation specifies involvement of multiple lymph node sites; if only one site is involved, use C84.10 instead
- •Sézary disease is a cutaneous T-cell lymphoma; ensure the diagnosis is clearly documented as Sézary disease and not other similar conditions like mycosis fungoides
Clinical Significance
Sezary disease involving lymph nodes at multiple sites indicates widespread nodal disease in this aggressive leukemic T-cell lymphoma. Multi-site lymphadenopathy is common in Sezary disease given its systemic nature with circulating malignant T-cells. This code captures the extent of nodal involvement which impacts staging and treatment decisions.
Documentation Requirements
- ✓Peripheral blood demonstrating circulating Sezary cells
- ✓Imaging documenting lymph node involvement at two or more distinct regions
- ✓Skin biopsy confirming cutaneous T-cell lymphoma
- ✓TNMB staging reflecting widespread nodal disease
- ✓Systemic treatment plan
Commonly Confused Codes
- •C84.11-C84.17 — Single-site Sezary disease codes: Use only when involvement is limited to one lymph node region
- •C84.19 — Sezary disease, extranodal: C84.18 is for multiple lymph node sites; C84.19 is for solid organ involvement
- •C84.08 — Mycosis fungoides, multiple sites: Distinct from Sezary disease