11th October 2020, Dr Chee L Khoo
There are a few “rare” medical diagnoses that are stuck in our minds since medical school days. They may be rare but it’s important not to miss them. Temporal arteritis, also known as giant cell arteritis (GCA) is one of those not so common conditions. It is actually not that rare. It is the most frequent primary systemic vasculitis with an annual incidence rate of 15–25 per 100,000 in Caucasians ≥50 years of age and it primarily affects medium- and large-sized vessels (1,2). When do you suspect GCA? And which clinical and laboratory findings can help to confirm the diagnosis? Which clinical and laboratory findings help to exclude the diagnosis?
Patients with GCA often present with non-specific symptoms. Although headache is a key symptom leading us to consider GCA, it is not that helpful as it is not discriminative enough. Besides, we see lots of headaches every day at the practice. Other features that may ring alarm bells for GCA include jaw claudication, limb claudication, double vision, temporal artery thickening (not very objective though), temporal tenderness and scalp tenderness. A previous diagnosis of polymyalgia rheumatica (PMR) and age younger than 70 years increase the likelihood of GCA.
What about laboratory findings? An ESR > 60 and a platelet count >400 increase the likelihood that the headache is GCA. Temporal artery biopsy (TAB; highly specific but with imperfect sensitivity) (3), vascular imaging (ultrasonography, computed tomography, magnetic resonance imaging, or positron emission tomography) (4) or a combination of these tests are recommended (4,5) all helps but are less of a gold standard than we used to think. Although the temporal artery biopsy (TAB) is often referred to as the gold standard, its sensitivity has been reported in the range of 40–87% (5,6). These further investigations should be selected based on pre-test probability (5,7). The difficulty in practice is how to quantify pre-test probability given only symptoms, signs, and, if available, laboratory features.
GCA is a clinical diagnosis. Establishing an accurate diagnosis of GCA can be difficult. A recent systematic review and meta-analysis of the diagnostic accuracy of symptoms, physical signs, and laboratory tests for GCA helps to quantify the features in terms of their likelihood of GCA (see table 1 below).
No single symptom, physical sign, or laboratory test is sufficient to completely rule in or rule out GCA. An additional imaging test or TAB is typically needed to make a confident diagnosis of GCA. If you are not that confident in your diagnostic acumen in relation to GCA, don’t fret. You are in good company. Over the years, when I suspect GCA and refer them to a vascular surgeon, they are always sceptical about my diagnosis but more times than not, I was proven right. GCA is one of those “do-not-miss” diagnosis. A delay in diagnosis can cause your patient his/her vision. The above table of important supporting symptoms, signs and basic laboratory findings helps us come to the diagnosis earlier.
References:
1. Diamantopoulos AP, Haugeberg G, Lindland A, Myklebust G. The fast-track ultrasound clinic for early diagnosis of giant cell arteritis significantly reduces permanent visual impairment: towards a more effective strategy to improve clinical outcome in giant cell arteritis? Rheumatology (Oxford). 2016; 55(1):66-70. doi:10.1093/rheumatology/kev289
2. Prior JA, Ranjbar H, Belcher J, et al. Diagnostic delay for giant cell arteritis – a systematic review and meta-analysis. BMC Med. 2017;15(1):120. doi:10. 1186/s12916-017-0871-z (Oxford). 2017;56(7):1154-1161. doi:10.1093/rheumatology/kex075
3. Banz Y, Stone JH. Why do temporal arteries go wrong? principles and pearls from a clinician and a pathologist. Rheumatology (Oxford). 2018;57(suppl 2):ii3-ii10. doi:10.1093/rheumatology/kex524
4. Dejaco C, Ramiro S, Duftner C, et al. EULAR recommendations for the use of imaging in large vessel vasculitis in clinical practice. Ann Rheum Dis. 2018;77(5):636-643. doi:10.1136/annrheumdis-2017-212649
5. Mackie SL, Dejaco C, Appenzeller S, et al. British Society for Rheumatology guideline on diagnosis and treatment of giant cell arteritis. Rheumatology (Oxford). 2020;59(3):e1-e23. doi:10.1093/rheumatology/kez672
6. Hunder GG, Bloch DA, Michel BA, et al. The American College of Rheumatology 1990 criteria for the classification of giant cell arteritis. Arthritis Rheum. 1990;33(8):1122-1128. doi:10.1002/art.1780330810
7. Dejaco C, Ramiro S, Duftner C, et al. EULAR recommendations for the use of imaging in large vessel vasculitis in clinical practice. Ann Rheum Dis. 2018;77(5):636-643. doi:10.1136/annrheumdis-2017-212649
8. van der Geest KSM, Sandovici M, Brouwer E, Mackie SL. Diagnostic Accuracy of Symptoms, Physical Signs, and Laboratory Tests for Giant Cell Arteritis: A Systematic Review and Meta-analysis. JAMA Intern Med. 2020 Oct 1;180(10):1295-1304. doi: 10.1001/jamainternmed.2020.3050. PMID: 32804186; PMCID: PMC7432275.