What is ICD-10 code C84.18?

C84.18 is the ICD-10-CM diagnosis code for Sezary disease, lymph nodes of multiple sites. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C84.18 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C84.18 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. C84.18 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. C84.18 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for C84.18?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For C84.18, V28 maps to Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic at RAF 4.209 while V24 mapped to Lymphoma and Other Cancers at RAF 0.675. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting C84.18?

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 Because C84.18 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

2026 ICD-10-CM C84.18: Sezary disease, lymph nodes

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Code lookupC84.18Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of lymphoid, hematopoietic and related tissue (C81-C96)

C84.18

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Sezary 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.

Buddy Insight

Sezary disease involving lymph nodes at multiple sites indicates widespread nodal disease in this aggressive leukemic T-cell lymphoma.

CMS-HCC V28

Mapped

HCC 17

Cancer Metastatic to Lung, Li...

RAF 4.209

CMS-HCC V24

Mapped

HCC 10

Lymphoma and Other Cancers

RAF 0.675

ACA/HHS

Mapped

HCC 10

HHS-HCC 10

Varies by metal level

ESRD/PACE

Mapped

HCC 10

Lymphoma and Other Cancers

RAF 0.111

RXHCC

Mapped

HCC 19

Lymphoma and Other Cancers

RAF 1.949

Code Book Path

Official

C84Mature T/NK-cell lymphomas

C84.1Sezary disease

C84.18Sezary disease, lymph nodes of multiple sites

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C84.18 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C84.18 in this effective period.

Related Child Codes

Official

C84.10Sezary disease, unspecified site

C84.11Sezary disease, lymph nodes of head, face, and neck

C84.12Sezary disease, intrathoracic lymph nodes

C84.13Sezary disease, intra-abdominal lymph nodes

C84.14Sezary disease, lymph nodes of axilla and upper limb

Includes

Official

ICD-10-CM does not list Includes notes for C84.18 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C84.18 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C84.18 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C84.18 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C84.18 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

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

MEAT Support

HCC Buddy guidance

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

Audit Caution

HCC Buddy guidance

Coding multiple individual site codes instead of the single multi-site code C84.18

Using unspecified site (C84.10) when imaging shows involvement of multiple lymph node regions

Not distinguishing between multiple nodal sites (C84.18) and extranodal organ involvement (C84.19)

Confusing Sezary disease with mycosis fungoides — peripheral blood analysis is key

Common Mistakes

HCC Buddy guidance

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

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is C84.18 an HCC code?

Yes. C84.18 (Sezary disease, lymph nodes of multiple sites) maps to Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic under the CMS-HCC V28 risk adjustment model (and Lymphoma and Other Cancers under V24), with a community non-dual aged RAF of 4.209. It is billable for payment year 2026.

Coder answer: C84.18 is billable and maps to V28 HCC 17, Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: C84.18
Description: Sezary disease, lymph nodes of multiple sites
HCC (V28): HCC 17 — Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic
RAF: 4.209
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 17, Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic

4.209

V24HCC 10, Lymphoma and Other Cancers

0.675

ESRDHCC 10, Lymphoma and Other Cancers

0.111

RxHCCHCC 19, Lymphoma and Other Cancers

1.949

Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. 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.

Work C84.18 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

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.

Coder workflow notes

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What This Code Means

C84.18 is the ICD-10-CM diagnosis code for sezary 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 Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic (HCC 17) with a community, non-dual, aged base RAF weight of 4.209. 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