Giant Cell Arteritis – Accuracy of H&P and Labs

Written by Clay Smith

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No single clinical or laboratory feature is enough to rule in or out giant cell arteritis (GCA, aka temporal arteritis). Vascular imaging or temporal artery biopsy is warranted. In the ED, we may need to start treatment prior to a definitive diagnosis being made.

Why does this matter?
GCA is a medium to large vessel vasculitis. Notably, it can inflame the temporal arteries and may lead to blindness if untreated. It is treated with a prolonged course of high dose glucocorticoids, which are not without side effects. It is diagnosed with history, exam, labs, imaging, and temporal artery biopsy (TAB). In the ED, we usually do the first three: history, exam, and labs. How good are these in diagnosing GCA?

This gives me a headache…
This article is a regular feature in ACEM, a concise review of previously published evidence with EM-relevance. In this case, it summarizes this systematic review. This included 68 studies, >14,000 patients. Included studies were heterogeneous, and none were performed in an ED setting. The gold standard also varied: TAB confirmation in 38 studies; clinical diagnosis in the rest. Keep in mind, TAB is not an ideal gold standard in itself and may have false negatives.

The strongest positive predictors (positive likelihood ratios) were:

  • Limb claudication: 6.0

  • Jaw claudication: 4.9

  • Temporal artery thickening: 4.7

  • Temporal artery loss of pulse: 3.3

  • Platelet count > 400 x 1000/μL: 3.8

  • Temporal tenderness: 3.1

  • ESR > 100 mm/h: 3.1

The strongest negative predictors (negative likelihood ratios) were:

  • ESR < 40 mm/h: 0.18

  • C reactive protein < 2.5 mg/dL: 0.38

  • Age < 70 years: 0.48

There is no single clinical or laboratory variable that clinches or rules out the diagnosis of GCA. Each variable (or combinations of variables) increases or decreases suspicion for GCA. Confirmation requires either vascular imaging (CT/MRI) or TAB. But even these advanced tests are imperfect. POCUS is an emerging new tool as well, as we will learn tomorrow. My advice in the ED is to consider GCA in patients with any of the above positive symptoms, ensure solid and prompt follow up, and start treatment.

Source
Diagnostic Accuracy of the History, Physical Examination, and Laboratory Testing for Giant Cell Arteritis. Acad Emerg Med. 2020 Dec 20. doi: 10.1111/acem.14196. Online ahead of print.

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