Giant cell arteritis (GCA) without concurrent polymyalgia rheumatica — a granulomatous large-vessel vasculitis affecting the aorta and its branches, most commonly the temporal and cranial arteries, in patients typically aged 50 or older.

Documentation tips

What should appear in the chart to support M31.6.

Source · Editorial brief grounded in 6 cited references ↓

• Document explicitly that polymyalgia rheumatica is absent or not diagnosed — this single distinction drives the M31.6 vs. M31.5 choice and prevents payer downcoding.
• Record the patient's age in the note; GCA coding carries implicit clinical validation expectations for age ≥50, and absence of this detail invites audit scrutiny.
• Capture inflammatory marker results (ESR and CRP values with units) and temporal artery biopsy or duplex ultrasound findings to substantiate medical necessity for vascular studies.
• If GCA-associated myopathy is also documented, code G72.9 (or the more specific myopathy code) as an additional diagnosis — the ICD-10-CM index cross-references M31.6 to myopathy in giant cell arteritis.
• Note the presenting cranial symptoms (headache, jaw claudication, visual changes, scalp tenderness) by name rather than as generic 'vascular symptoms' to support specificity.

Related CPT procedures

Procedure codes commonly billed with M31.6. Linking the right diagnosis to the right procedure is what establishes medical necessity.

Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis

Common coding pitfalls

The recurring mistakes coders make with M31.6 and adjacent codes.

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

• Assigning M31.5 when PMR is not explicitly documented — shoulder or hip girdle pain alone does not constitute PMR; provider documentation of both diagnoses is required before using M31.5.
• Using I77.6 (Arteritis, unspecified) when the record clearly states giant cell arteritis or temporal arteritis — both index to M31.6, making I77.6 a less specific and potentially denying code.
• Omitting M31.6 as a secondary diagnosis when GCA-related myopathy is the primary complaint presented in an orthopedic setting — the index explicitly maps myopathy in GCA to M31.6.
• Confusing M31.4 (Aortic arch syndrome/Takayasu) with M31.6 when large-vessel GCA involves the aorta — Takayasu arteritis is a distinct entity with its own code; GCA of the aorta in patients ≥50 maps to M31.6.

Clinical context

Source · Editorial summary grounded in 6 cited references ↓

Sibling codes

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