To Biopsy or Not to Biopsy - That is the Question

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At the CRA meeting today, Dr. Simon Carette (University of Toronto) presented issues influencing the decision to perform a temporal artery biopsy (TAB) in patients with giant-cell arteritis (GCA). The question - Do they change the course of management? Does our management really change in patients who are TAB positive versus negative?

Temporal artery biopsy is THE gold standard to diagnose GCA. The specificity of TAB is … 100%. The positive predictive value is … 100%. The problem is the sensitivity of the test. The literature suggests a variance in the sensitivity of 15-40%. However, these studies were retrospective and based on case series, not prospective studies. This raises the question, did the patients actually have the disease?

Why the low sensitivity? Possible reasons include:

The length of the specimen: 1 cm is generally agreed on
The number of cuts: More important than the length is the number of cuts the pathologist reviews. This is important to identify the presence of skip lesions.
The duration of steroid therapy prior to biopsy can affect the result. It is generally agreed that the biopsy should be obtained within 2-4 weeks of the initiation of prednisone.

The real question as to whether TAB will be helpful is, “What is your pre-test probability?" Consider the following two scenarios: A 52-year-old woman with new-onset HA and an ESR of 54 versus an 83-year-old woman with new-onset HA, symptoms of PMR, jaw claudication, sudden vision loss, and an ESR of 115. In which of these patients is the pre-test probability for GCA higher? It’s pretty obvious, isn’t it.

What are the alternatives to TAB? MRI and U/S both have a very good negative predictive value (up to 98%). Because of their high negative predictive value (NPV) they may negate the need for TAB especially in patients with a low pretest probability. However, due to their low positive predictive value (<50%), these tests are often inconclusive for making a diagnosis. Furthermore, U/S is largely operator dependant and MRI for GCA is not widely available.

The question remains, will TAB change your management? If your pre-test probability is high and you would still treat independently of the results of the biopsy, you would be justified not do the biopsy. If the pre-test probability is low, why bother doing a biopsy in the first place? In this group of patients, an U/S or MRI may be an alternative to rule out GCA. In patients with an intermediate pre-test probability, a TAB is still required.

More reports from 2015 CRA & AHPA