ICD-10 code M31.6: Other giant cell arteritis

Key Takeaways

ICD-10 code M31.6 is the billable diagnosis code for other giant cell arteritis (temporal arteritis without polymyalgia rheumatica), valid for FY 2026.

Use M31.5 when giant cell arteritis occurs with polymyalgia rheumatica; use M31.6 when PMR is absent.

Documentation must confirm GCA pathology, typically via temporal artery biopsy, elevated ESR/CRP, and clinical symptoms such as headache and jaw claudication.

Pabau’s claims management software and digital intake forms help rheumatology and ophthalmology practices capture M31.6 accurately at every encounter.

ICD-10 code M31.6 is the billable ICD-10-CM diagnosis code for other giant cell arteritis — giant cell (temporal) arteritis without polymyalgia rheumatica. It’s valid for FY 2026 reimbursement, sits in the musculoskeletal and connective tissue disorders block (M30-M36), and requires documentation that explicitly rules out polymyalgia rheumatica to distinguish it from M31.5.

ICD-10 code M31.6: Definition and clinical overview

Incomplete documentation, more than an incorrect diagnosis, is what causes most M31.6 claim denials. Payers routinely reject claims when records lack the biopsy result, inflammatory marker values, or explicit exclusion of polymyalgia rheumatica.

ICD-10 code M31.6 is the billable, specific ICD-10-CM diagnosis code for “Other Giant Cell Arteritis.” It falls under Chapter 13 (Diseases of the Musculoskeletal System and Connective Tissue, M00-M99), block M30-M36 (Systemic Connective Tissue Disorders) — the same broad chapter that rheumatology and sports medicine practices use for other musculoskeletal and connective tissue codes.

According to the CMS, M31.6 is valid and billable for reimbursement purposes in fiscal year 2026.

Giant cell arteritis is a granulomatous inflammation of large and medium blood vessels, most commonly the temporal artery. It predominantly affects adults over age 50. When GCA presents without concurrent polymyalgia rheumatica, M31.6 is the correct code. When polymyalgia rheumatica accompanies GCA, coders must use M31.5 instead.

Synonyms and clinical inclusions under ICD-10 code M31.6

M31.6 encompasses several clinical presentations beyond the most familiar label of temporal arteritis. Coders and clinicians both need to know which conditions fall under this single code to avoid incorrect code selection or unbundling.

According to ICD10Data.com, the following synonyms and inclusions are accepted under M31.6:

• Giant cell arteritis (the broad category, without PMR)
• Temporal arteritis (the most common clinical presentation)
• Cranial arteritis
• Granulomatous arteritis
• Horton disease
• Anterior ischemic optic neuropathy (arteritic), also documented as A-AION
• Arteritic anterior ischemic optic neuropathy

The inclusion of arteritic anterior ischemic optic neuropathy (A-AION) is significant. Ophthalmologists managing GCA-related vision loss should document that the AION is arteritic in origin, not non-arteritic (N-AION), to support M31.6.

Non-arteritic AION uses a separate code from the H47 range. Without the qualifier “arteritic” in the clinical note, the coder cannot defensibly assign M31.6 for optic neuropathy presentations.

M31.5 vs M31.6: Choosing the correct ICD-10 code for giant cell arteritis

The single most common coding error in giant cell arteritis encounters is using M31.6 when M31.5 is correct, or vice versa. The distinction rests entirely on whether polymyalgia rheumatica (PMR) is present alongside the arteritis.

Rheumatologists should note that PMR and GCA frequently coexist, with estimates suggesting PMR accompanies GCA in roughly 40-60% of cases. If the physician documents both conditions in the same visit, M31.5 takes precedence.

If the note describes only GCA symptoms (temporal headache, jaw claudication, scalp tenderness, elevated inflammatory markers) without PMR features such as proximal limb girdle pain and morning stiffness, M31.6 is appropriate. Practices tracking functional status in these patients can use a muscular strength test template to document proximal girdle involvement at each visit.

Accurate diagnostic code documentation at the encounter level prevents downstream audit risk. Structured templates within an EMR system reduce the chance of this distinction being missed during a busy clinical day.

Documentation requirements to support ICD-10 code M31.6 at audit

A billable M31.6 claim is only as strong as the documentation behind it. Payers, including Medicare, expect specific clinical evidence in the record before approving reimbursement for giant cell arteritis encounters.

The following elements should appear in the clinical note for every M31.6 encounter:

• Chief complaint and symptom narrative: Document temporal headache, scalp tenderness, jaw claudication, vision changes, or constitutional symptoms (fever, fatigue, weight loss).
• Temporal artery findings: Note tenderness, thickening, nodularity, or absent pulse on palpation. Record the result of temporal artery biopsy when performed, including pathology report reference.
• Inflammatory markers: Record erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) values with reference ranges. GCA typically presents with ESR above 50 mm/hr and elevated CRP.
• PMR exclusion: Explicitly state whether polymyalgia rheumatica is present or absent. Without this, a reviewer cannot confirm M31.6 over M31.5.
• Ophthalmologic involvement: When A-AION is suspected or confirmed, document it as arteritic and record visual acuity, optic disc examination findings, and fluorescein angiography results where applicable.
• Treatment initiated: Record corticosteroid therapy initiation (typically high-dose prednisone), dosage, clinical rationale, and any escalation to infusion-based biologic therapy billed under J9312 in refractory cases.

Practices that maintain structured patient records with standardized GCA documentation templates can retrieve audit-ready evidence without reconstructing the encounter from memory. This matters in rheumatology, ophthalmology, and neurology practices where M31.6 encounters involve multi-specialist input.

The compliance documentation requirements that apply across regulated clinical settings are directly relevant here: complete, contemporaneous records are the first line of defense in any payer audit. For GCA, this means capturing biopsy results, lab values, and the PMR distinction in the same visit note, not as an addendum days later.

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Associated CPT codes and procedures for giant cell arteritis

ICD-10 code M31.6 is a diagnosis code. It pairs with procedure codes (CPT) to form a complete claim. Understanding which CPT codes typically accompany M31.6 helps coders build accurate claims and avoids medical necessity denials.

According to the AAPC Codify ICD-10-CM reference, common CPT codes paired with M31.6 include:

For practices using the AAPC CPT-to-ICD-10 crosswalk, verifying medical necessity linkages between CPT 37609 and M31.6 before claim submission prevents denials at adjudication. Most payers require that the diagnosis code directly supports the procedure performed.

Ophthalmology practices may also bill for visual field testing (CPT 92083) or fundus photography (CPT 92250) when A-AION is the presenting finding. In these cases, M31.6 serves as the primary diagnosis if GCA is confirmed, with optic neuropathy serving as an additional code when required by the payer.

ICD-10 code M31.6 coding guidelines and sequencing rules

The CDC/NCHS ICD-10-CM official guidelines provide the sequencing framework coders must follow when assigning M31.6. Getting the principal versus additional diagnosis distinction right affects MS-DRG grouping in inpatient settings and E/M level justification in outpatient encounters.

Principal diagnosis in inpatient settings

When a patient is admitted specifically for GCA management (for example, for high-dose IV corticosteroid initiation or suspected vision-threatening arteritis), M31.6 is appropriate as the principal diagnosis. MS-DRG assignment will flow from this, typically grouping under DRG 553-555 (Bone Diseases and Arthropathies) depending on comorbidity and complication status.

Secondary diagnosis in outpatient settings

In outpatient encounters where GCA is a known chronic condition being monitored, M31.6 is sequenced as the reason for the visit or as an additional diagnosis, depending on what drove the encounter. If the patient presented for a GCA follow-up, M31.6 is principal. If GCA is incidentally relevant during a general medicine visit, it may be additional.

Understanding patient compliance is directly connected to follow-up coding: patients who miss corticosteroid follow-ups may present later with acute complications, changing the encounter’s principal diagnosis entirely.

Combination coding rules

M31.6 does not have any listed Type 1 Excludes or Type 2 Excludes notes in the ICD-10-CM tabular list that prevent it from being used with most other musculoskeletal or vascular codes. However, coders must not assign both M31.5 and M31.6 in the same encounter: these are mutually exclusive based on PMR status.

When ophthalmologic complications are present, additional codes from the H47 range may be assigned alongside M31.6 to capture the full clinical picture, provided the documentation supports both.

ICD-9 to ICD-10 crosswalk for giant cell arteritis

Practices transitioning historical records, running retrospective analyses, or handling appeals involving pre-October 2015 claims will encounter the ICD-9-CM legacy code for giant cell arteritis.

The ICD-9-CM code 446.5 was a broader code that did not distinguish between GCA with and without polymyalgia rheumatica. The ICD-10-CM transition introduced the M31.5 / M31.6 split to improve clinical specificity.

For historical reference and crosswalk purposes, 446.5 maps to M31.6 as the approximate equivalent. Do not use 446.5 for any current billing: it is retired and payers will reject claims coded to ICD-9.

Practices dealing with vascular condition codes such as H34.9 in historical patient records should note that the ICD-9 to ICD-10 transition requires clinical review, not just automated crosswalk substitution. The coder should confirm which current code (M31.5 or M31.6) best reflects the clinical reality of the original encounter before assigning the crosswalk code.

How EMR and practice management software supports M31.6 coding accuracy

Practices managing GCA patients across rheumatology, ophthalmology, and neurology teams need documentation systems that reduce the risk of coding errors at the point of care, not during a post-visit correction cycle.

Pabau’s claims management software supports accurate ICD-10 diagnostic code capture by allowing practices to configure encounter templates with mandatory fields for GCA-specific clinical data: biopsy status, ESR/CRP values, PMR exclusion documentation, and ophthalmic involvement.

These fields prompt clinicians to complete the documentation that payers require before a claim is submitted, rather than finding out at audit that something was never recorded.

For new patient encounters, digital intake forms can capture symptom onset, prior diagnoses, and current medications before the consultation begins, giving the treating clinician a pre-structured foundation for the GCA assessment note. This is especially valuable in ophthalmology practices where A-AION may be the presenting symptom and the GCA diagnosis is reached during the same encounter.

Practices with multi-location teams or shared GCA patient panels benefit from centralized compliance management tools that flag incomplete encounters before claims are batched. A single missing PMR documentation field is enough to convert a clean M31.6 claim into a denial or a request for additional documentation.

Conclusion

Giant cell arteritis without polymyalgia rheumatica is a clinically urgent condition that demands precise documentation and equally precise coding. ICD-10 code M31.6 is the correct, billable code for these encounters in FY 2026, but reimbursement depends on records that explicitly confirm GCA pathology, document inflammatory markers, and distinguish the case from M31.5.

Practices that build M31.6 documentation requirements directly into their clinical workflow reduce denial rates and audit exposure. Pabau’s practice management software helps rheumatology, ophthalmology, and neurology teams capture every required data point at the encounter level. To see how Pabau handles diagnostic code workflows, book a demo.

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