G73.1
BillableLambert-Eaton syndrome in neoplastic disease
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is G73.1 an HCC code?
Yes. G73.1 maps to Myasthenia Gravis/Myoneural Conditions and Guillain-Barre under the CMS-HCC V28 risk adjustment model (and Myasthenia Gravis/Myoneural Conditions and Guillain-Barre Syndrome 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 G73.1
For G73.1 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 G73.1 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
G73.1 is the ICD-10-CM diagnosis code for lambert-eaton syndrome in neoplastic disease. Lambert-Eaton syndrome occurring as a complication of cancer. This is an autoimmune disorder affecting the connection between nerves and muscles, triggered by malignancy. G73.1 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering diseases of myoneural junction and muscle (g70-g73).
Under the CMS-HCC V28 risk adjustment model, G73.1 maps to Myasthenia Gravis/Myoneural Conditions and Guillain-Barre (HCC 196) with a community, non-dual, aged base RAF weight of 0.402. Under the older CMS-HCC V24 model, G73.1 maps to Myasthenia Gravis/Myoneural Conditions and Guillain-Barre Syndrome (HCC 75) with a community, non-dual, aged base RAF weight of 0.425. 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.
Always code the underlying neoplasm first, followed by this code to show the relationship between cancer and the syndrome. Because G73.1 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 G73.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Always code the underlying neoplasm first, followed by this code to show the relationship between cancer and the syndrome
- •Document the type of cancer and whether it is small cell lung cancer, which is the most common association
Clinical Significance
Lambert-Eaton syndrome in neoplastic disease is a paraneoplastic condition most commonly associated with small cell lung cancer, where cancer triggers an autoimmune attack on presynaptic calcium channels. This diagnosis indicates both malignancy and a significant neurological complication, reflecting extremely complex patient care. Capturing this code alongside the underlying malignancy is critical for accurate risk adjustment.
Documentation Requirements
- ✓Documentation of the underlying neoplasm (most commonly small cell lung cancer)
- ✓Clinical features of Lambert-Eaton syndrome: proximal weakness, autonomic dysfunction, hyporeflexia
- ✓Electrodiagnostic confirmation: incremental response on repetitive nerve stimulation
- ✓Voltage-gated calcium channel antibody testing results
- ✓The underlying neoplasm code must be sequenced first
- ✓Provider's explicit documentation linking the Lambert-Eaton syndrome to the malignancy