ICD-10 code M31.5: Giant cell arteritis with polymyalgia rheumatica

Key takeaways

ICD-10 code M31.5 is a billable ICD-10-CM diagnosis code for giant cell arteritis with polymyalgia rheumatica.

The code needs both conditions documented, so using it without a stated PMR diagnosis is an audit risk.

M31.6 covers giant cell arteritis without polymyalgia rheumatica, and mixing up the two codes is the most common error here.

M35.3 carries an Excludes1 note for M31.5, so the two codes are never reported on the same claim.

Practice management software like Pabau validates code entry at the point of care, so errors surface before submission.

ICD-10 code M31.5 is a billable, specific ICD-10-CM diagnosis code for giant cell arteritis with polymyalgia rheumatica. The 2026 edition took effect on October 1, 2025. The code is valid for claim submission and reimbursement across US payer systems.

M31.5 sits in the M30-M36 block (Systemic connective tissue disorders), under the M31 subcategory for other necrotizing vasculopathies. Both CMS and the National Center for Health Statistics maintain it. The official description reads: Giant cell arteritis with polymyalgia rheumatica.

The code needs both diagnoses in the record. If polymyalgia rheumatica is not stated by the treating clinician, M31.6 is the correct code instead. That single distinction drives most denials in this category.

M31.5 code details at a glance

The table below summarizes the reference data for the code. Confirm edition validity each October, when CMS publishes its annual update.

You can check the current edition status with the CDC ICD-10-CM tool, which mirrors the official tabular list for each update cycle. Run that check at the start of every fiscal year, before the first claims go out.

What is giant cell arteritis with polymyalgia rheumatica?

Giant cell arteritis (GCA) is chronic inflammation of large and medium-sized blood vessels, most often the temporal arteries and branches of the aorta. It also goes by temporal arteritis, cranial arteritis, and Horton’s arteritis.

Polymyalgia rheumatica (PMR) is a related inflammatory condition. It causes pain and stiffness in the shoulders, neck, upper arms, hips, and thighs.

The two conditions co-occur often. Studies suggest 40% to 60% of GCA patients also present with PMR. That overlap is why ICD-10-CM carries a dedicated combination code. GCA with PMR affects adults over 50, with peak incidence between ages 70 and 80.

Key clinical features that support an M31.5 diagnosis:

• New-onset headache, typically temporal or occipital
• Scalp tenderness or temporal artery thickening on palpation
• Jaw claudication, meaning pain with chewing
• Visual disturbance or transient vision loss
• Proximal muscle aching and morning stiffness, which is the PMR component
• Elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP)
• Temporal artery biopsy showing giant cell infiltration, where one was performed

Girdle stiffness often sends these patients to physical therapy practices first, so the arteritis diagnosis can arrive weeks after the muscle symptoms do.

Temporal artery biopsy remains the gold standard for confirming GCA. The American College of Rheumatology accepts a clinical diagnosis without biopsy where imaging or presentation is strongly suggestive. For code assignment, what matters is that both GCA and PMR are documented by the treating clinician.

Inclusion terms and synonyms

The ICD-10-CM tabular list treats these terms as applicable to M31.5. Coders will meet any of them in clinical documentation, and all of them map to the same code:

• Giant cell arteritis with polymyalgia rheumatica
• Temporal arteritis with polymyalgia rheumatica
• Cranial arteritis with polymyalgia rheumatica
• Horton’s arteritis with polymyalgia rheumatica
• GCA with PMR

These inclusion terms come from the ICD-10-CM Alphabetic Index. The index path runs Arteritis, giant cell, with polymyalgia rheumatica, which resolves to M31.5.

Exclusion notes: what the code does not cover

Knowing what the code excludes matters as much as knowing when to use it. Coding the wrong condition here creates audit exposure and payer-level rejections. Compliance management tools that flag conflicts at the point of entry cut that risk down.

The tabular list settles the pairing with M35.3 outright. Its Excludes1 note reads “polymyalgia rheumatica with giant cell arteritis (M31.5)”, so the two codes are officially excluded from being reported together. The PMR component is already captured inside the combination code.

M31.5 vs M31.6: key differences

The one thing separating M31.5 from M31.6 is whether polymyalgia rheumatica is documented. Getting that wrong is the most common coding error in the giant cell arteritis family. The table below sets the distinction out.

The AAPC code lookup lists both codes as billable within the M31 category. Searching the index for “giant cell arteritis” alone routes to M31.6. Confirm the PMR documentation before you move the claim to M31.5.

Sibling codes in the M31 category

M31 covers other necrotizing vasculopathies inside the wider M30-M36 block. Knowing the siblings helps coders move through the category without landing on the wrong fourth character.

• M31.0 — Hypersensitivity angiitis (Goodpasture’s syndrome)
• M31.1 — Thrombotic microangiopathy
• M31.2 — Lethal midline granuloma
• M31.3 — Wegener’s granulomatosis (non-billable header, coded to M31.30 or M31.31)
• M31.4 — Aortic arch syndrome (Takayasu’s arteritis)
• M31.5 — Giant cell arteritis with polymyalgia rheumatica
• M31.6 — Other giant cell arteritis
• M31.7 — Microscopic polyangiitis
• M31.8 — Other specified necrotizing vasculopathies
• M31.9 — Necrotizing vasculopathy, unspecified

Only M31.3 needs a fifth character. Use M31.30 for Wegener’s granulomatosis without renal involvement, and M31.31 where the kidneys are involved. M31.3 on its own is a non-billable header code.

The WHO ICD-10 browser shows the international classification that ICD-10-CM is derived from. The M31.5 parent structure is the same in both.

Documentation requirements

Thin documentation is the main cause of M31.5 rejections. Both halves of the combination code have to be supported in the clinical record. Digital intake forms and structured notes catch what a free-text chart tends to leave out.

These elements should be in the medical record before M31.5 is assigned:

• Explicit GCA diagnosis. The clinician has to name giant cell arteritis, temporal arteritis, or cranial arteritis as a confirmed or working diagnosis. A symptom description is not enough.
• Explicit PMR diagnosis. Polymyalgia rheumatica needs its own entry. Proximal muscle aching on its own will not support the code.
• Symptom documentation. New headache, jaw claudication, scalp tenderness, visual symptoms, or girdle pain, supporting each half of the diagnosis.
• Lab findings. Record the ESR and CRP values themselves rather than the word “elevated”, since thresholds vary by laboratory reference range.
• Biopsy results. Where a temporal artery biopsy was performed, record the finding. A negative biopsy still allows M31.5 if clinical criteria are met and the clinician documents the reasoning.
• Treatment plan. Corticosteroid initiation or tapering, documented in line with GCA and PMR management.

Rheumatology encounter templates that prompt for all six cut down on retrospective physician queries. Those queries arrive weeks later, when nobody remembers the visit.

Once the encounter is written up, record retention rules govern how long that chart stays reachable for an audit. Tying documentation templates to code-specific requirements, the way practice compliance workflows do, makes those audits far more predictable.

Coding tips and common pitfalls

Rheumatology billers hit a predictable set of errors with this code. These five account for most rejections and audit findings in the category.

• Using M31.5 when PMR is suspected but not documented. Clinical suspicion does not justify the combination code. The physician has to state the diagnosis. Where only GCA is confirmed, use M31.6.
• Adding M35.3 alongside M31.5. The Excludes1 note rules the pairing out, and payers read the duplicate as unbundling.
• Defaulting to M31.6 for every GCA encounter. Coders who never query the chart for PMR will under-code by habit. Query the physician when the chart mentions shoulder or hip girdle complaints.
• Reaching for the unspecified code M31.9. M31.5 is billable and specific. Using M31.9 where documentation supports M31.5 costs reimbursement and invites a compliance finding.
• Entering through the wrong index term. Arteritis > giant cell > with polymyalgia rheumatica gives M31.5. Entering under Polymyalgia > rheumatica gives M35.3.

Diagnostic code validation flags these patterns before a claim leaves the practice. That pays off most where older patients dominate the caseload, as they do in practices running longevity clinic software.

Structured coding workflows protect the revenue side too, since every avoidable denial resurfaces in patient collections a month later. Code validation is worth testing on any demo, and it separates otherwise similar EMR options for small practices.

Alphabetic index entry paths

Coders reach M31.5 through several routes in the ICD-10-CM Alphabetic Index. Knowing them prevents mislookups that land on M31.6 or M35.3:

• Arteritis > giant cell > with polymyalgia rheumatica = M31.5
• Arteritis > temporal > with polymyalgia rheumatica = M31.5
• Horton’s disease > with polymyalgia rheumatica = M31.5
• Giant cell arteritis > with polymyalgia rheumatica = M31.5

Entering polymyalgia rheumatica as the primary index term lands on M35.3 instead. The coder has to enter through the arteritis path and confirm the PMR qualifier to reach M31.5.

How Pabau keeps M31.5 documentation and claims aligned

M31.5 usually goes wrong at the point of care rather than at the coding desk. The clinician sees both conditions, treats both, and writes up one. By the time the coder opens the chart, the PMR diagnosis exists only in the physician’s memory.

Practice management software like Pabau moves that check forward, to the moment the note is still open. A rheumatology workflow for this code covers five things:

1. Structured encounter templates that prompt for the GCA and PMR diagnoses separately in the assessment, not just the problem list
2. Code lookup at charge entry that surfaces M31.5 on a search for “giant cell arteritis” and asks for PMR confirmation first
3. Combination code alerts that block M31.5 and M35.3 from being entered together, killing the unbundling error at source
4. Lab result integration that attaches ESR and CRP values to the encounter, so medical necessity is evidenced at submission
5. Claim scrubbing rules that check payer-specific edits and documentation requirements before the claim goes out

Pabau’s claims management software handles diagnostic code entry and claim workflow for multi-specialty practices. Structured encounter notes hold both diagnoses the code requires, so payer queries have somewhere to land.

Pabau Scribe, our AI scribe, sits on top of that. It turns the consultation into a structured note, prompting for the GCA diagnosis, the PMR diagnosis, and the lab values that hold the claim up. You can see how AI-assisted documentation fits a day in a rheumatology practice.

Catch coding errors before the claim goes out

Pabau helps rheumatology and multi-specialty practices build documentation workflows that capture what M31.5 needs. Both diagnoses get recorded while the patient is still in the room.

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Conclusion

The choice between M31.5 and M31.6 is settled in the encounter note, not at charge entry. If the clinician names both diagnoses, the combination code is defensible. If not, no coder can rescue it afterwards.

So treat this as a documentation habit rather than a coding one. Put the PMR prompt inside the rheumatology template and the right code follows on its own. The trade-off is a few extra seconds in the assessment field, against a denial that costs an hour to appeal.

Get that habit in place and M31.5 stops being a category you audit and starts being one you trust. Book a demo to see how Pabau structures rheumatology documentation and claims.

Continue your research

Coding giant cell arteritis when PMR is absent? M31.6 covers the standalone code and what the chart has to show.

Need the standalone polymyalgia rheumatica code? M35.3 sets out when PMR is reported on its own.

Ruling out Takayasu arteritis instead? M31.4 explains the aortic arch syndrome code and its documentation.

Documenting polyarteritis nodosa? M30.0 walks through the code and the findings payers expect.

Coding vasculitis in a younger patient? M30.2 walks through juvenile polyarteritis and its documentation rules.

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