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Contextualizing temporal arterial magnetic resonance angiography in the diagnosis of giant cell arteritis: a retrospective cohort study.

OBJECTIVES
Imaging modalities have become common in evaluating patients for a possible diagnosis of Giant Cell Arteritis (GCA). This study seeks to contextualize how temporal arterial magnetic resonance imaging (TAMRA) can be used in facilitating the diagnosis of GCA.


METHODS
A retrospective cohort study was performed upon patients who had been previously referred to a rheumatologist for evaluation of possible GCA in Hamilton, Ontario, Canada. Data including clinical features, inflammatory markers, imaging, and biopsy results were extracted. Multivariable logistic regression model to predict the diagnosis of GCA. Using these models, the utility of TAMRA in series with or in parallel to clinical evaluation was demonstrated across the cohort as well as in subgroups defined by biopsy and imaging status.


RESULTS
268 patients had complete data. Those diagnosed with biopsy- and/or imaging-positive GCA were more likely to demonstrate classic features including jaw claudication and vision loss. Clinical multivariable modelling allowed for fair discriminability (receiver-operator characteristic (ROC) 0.759, 95% CI 0.703-0.815) for diagnosing GCA; there was excellent discriminability in facilitating the diagnosis of biopsy-positive GCA (ROC 0.949, 0.898-1.000). When used in those with a pre-test probability of 50% or higher, TAMRA had a PPV of 93.0%; in those with a pre-test probability of 25% or less TAMRA had an NPV of 89.5%.


CONCLUSION
In those with high disease probability, TAMRA can effectively rule in disease (and replace temporal artery biopsy). In those with low to medium probability, TAMRA can help rule out the disease, but this continues to be a challenging diagnostic population.