M31.7 identifies microscopic polyangiitis (MPA), a systemic ANCA-associated vasculitis targeting small vessels — and occasionally medium vessels — with a predilection for renal and pulmonary involvement.

Documentation tips

What should appear in the chart to support M31.7.

Source · Editorial brief grounded in 5 cited references ↓

• Confirm the specific diagnosis as microscopic polyangiitis — not simply 'ANCA vasculitis' or 'polyarteritis' — before assigning M31.7; the Alphabetic Index distinguishes these explicitly.
• Document ANCA status (MPO-ANCA/p-ANCA positivity is typical for MPA) and the organs involved (kidneys, lungs, peripheral nerves, skin) to support medical necessity and specificity.
• When MPA is causing a secondary condition (e.g., glomerulonephritis, polyneuropathy), sequence M31.7 as the underlying etiology and the manifestation code (e.g., N05.9, G62.9) as an additional diagnosis per etiology/manifestation convention.
• Record immunosuppressive or biologic therapy in use — this affects surgical risk, infection risk coding, and prior authorization documentation for any concurrent procedures.
• Distinguish MPA from granulomatosis with polyangiitis (M31.3-) and eosinophilic granulomatosis with polyangiitis (M30.1) in the clinical note; these are separate diagnoses with separate codes and cannot be coded concurrently with M31.7.

Common coding pitfalls

The recurring mistakes coders make with M31.7 and adjacent codes.

Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓

• Assigning I77.82 (ANCA vasculitis) instead of M31.7 when the provider has documented a confirmed diagnosis of microscopic polyangiitis — I77.82 has a Type 2 Excludes note for M31.7 and should not be used when MPA is specified.
• Confusing microscopic polyangiitis (M31.7) with polyarteritis nodosa (M30.0) — the Excludes1 note at M31.7 bars simultaneous coding; these are distinct entities and cannot be coded together.
• Using M30.0 for a patient whose record says 'microscopic polyarteritis' — the Alphabetic Index directs 'microscopic polyarteritis' to M31.7, not M30.0.
• Omitting manifestation codes for organ-specific complications (glomerulonephritis, polyneuropathy) when MPA is the underlying cause — the etiology/manifestation pair is required and improves clinical picture for payers.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Inclusion & exclusion notes

Per the official ICD-10-CM Tabular List.

Source · CDC ICD-10-CM Official Tabular List · 2026

Sibling codes

Other billable codes under M31 (laterality / anatomic variants).