In patients with suspected giant cell arteritis (GCA), there is no single clinical or laboratory feature likely to shift pretest probability sufficiently that further confirmatory testing is not required, a new study has shown.
A systematic review and meta-analysis of the evidence, comprising 68 studies and over 14,000 patients, estimated likelihood ratios (LR) for the diagnostic accuracy of about 20 symptoms and a similar number of physical and laboratory findings associated with GCA.
It found features that should upgrade the level of suspicion for GCA included limb claudication (LR 6.01), jaw claudication (LR 4.90), various temporal artery abnormalities (LR range 1.93 – 4.70); platelets >400 × 103/μL (LR 3.75), elevated ESR >40 mm/h (LR range 1.49-3.11), and anterior ischaemic optic neuropathy (LR LR 1.73).
Features that should downgrade the level of suspicion for GCA were age ≤70 years, CRP in the reference range or <2.5 mg/dL; and an ESR <40mm/h.
The investigators said that while the LRs would not render further investigation for GCA unnecessary, they “may inform clinical decisions, including selection and timing of investigations, and whether to immediately commence high-dose glucocorticoid therapy or await further test results.”
They noted that some features considered classic for GCA such as headache and scalp tenderness had limited use for upgrading or downgrading the clinical probability of GCA.
However it did not mean those symptoms were irrelevant.
“Headache is important in prompting suspicion of GCA and onward referral to a specialist, but once that referral decision has been made, clinicians should be cautious about overvaluing the diagnostic significance of headache and should evaluate patients for the other features identified in our meta-analysis as informative for a final diagnosis of GCA.”
Commenting on the JAMA study, Sydney vasculitis specialist Dr Anthony Sammel told the limbic it was a well designed and useful study.
“It probably confirms what we know – it probably doesn’t introduce anything new – but I think it really challenges the paradigm that some clinicians feel that their clinical assessment is good enough for a diagnosis.”
He said it never fails to surprise him how atypical GCA presentations can be.
“The other important thing it shows is that taking a history and an examination, while they are not perfect, they do assist [in increasing or decreasing the pre-test probability].”
“So taking a good history around jaw claudication in particular is really important. Examining the temporal arteries is also important and the finding of an abnormality over the temporal artery is an important feature in terms of making the diagnosis more likely.”
“Some clinicians feel they don’t need to go and perform confirmatory testing with either a biopsy or imaging. This study once again challenges that view and says actually our clinical tools, which is our history taking and physical examination and basic blood tests, are not good enough to confirm or refute a diagnosis alone.”
An Invited Commentary in JAMA said insights from the study would “refine pretest probability determinations and guide difficult point-of-care decisions, such as committing a frail patient to a temporal artery biopsy or deciding whether to start corticosteroid treatment immediately or await test results.”