Page 344 - The Vasculitides, Volume 1: General Considerations and Systemic Vasculitis

318 Vanessa Quick and John Kirwan

of GCA of 68% [77] emphasizing the difficulty in ascertaining a conclusive histopathologic
diagnosis even when the clinical features are highly suggestive.

Laboratory Studies

Blood Studies
Acute phase markers of inflammation are often significantly elevated, and a normocytic

normochromic anemia and thrombocytosis may be present [78], as may elevation of liver
transaminase levels [79], while the serum albumin level may be depressed. The presence of
rheumatoid factor, antinuclear (ANA) and other autoantibodies are not present in greater
frequency than in the general population; however ascertainment of serum ANCA may help
to differentiate GCA from other forms of vasculitis. Although the ESR has historically been
the acute phase measure of choice in the diagnosis of GCA, up to a quarter of patients may
have a normal value [47, 80-82] and elevation of the C-reactive protein (CRP) is a better
predictor of obtaining a diagnostic TAB [9, 81, 83, 84]; the combination of an elevated CRP
and positive TAB render the highest sensitivity and specificity for the diagnosis of GCA.
Only 1 in 119 (.8%) patients to 7 in 177 (4%) patients [81, 84] with GCA presented with both
normal ESR and CRP levels, however such findings may be subject to selection and referral
bias. We routinely measure the CRP and plasma viscosity in all patients with suspected GCA
since the latter has the advantage of paralleling the ESR, uninfluenced by age, gender,
hematocrit or time to analysis.

Temporal Artery Biopsy
Temporal artery biopsy has been the gold standard test representing definitive

pathological diagnosis [7, 13, 14, 38, 46, 55]. Performed correctly, TAB carries a low
procedural risk of significant complications [77], and a positive result removes later doubts
about diagnosis, particularly if treatment causes complications [85, 86] or if the patient fails
to respond promptly to therapy [87], whereas a negative biopsy is important in averting long
term risk of empiric glucocorticoids [88]. Up to one-third of clinicians surveyed did not
recommend TAB for the diagnosis of GCA [89] possibly because it did not alter the
perceived necessity of empiric therapy when the result was inconclusive or negative [90-92].
The true sensitivity of unilateral TAB was 87% employing Bayesian analysis [93] with a
variation in sensitivity of 24% to 94% in clinical cohorts [87]. The likelihood of a false-
negative TAB may be in?uenced by the length of the specimen, the duration of prior
glucocorticoid therapy, pathological sectioning techniques and the presence of predominantly
non-cranial disease. Retrospective reviews suggest a post-fixation biopsy length of 1 to 2
centimeters (cm) is adequate [94-97], but a length of greater than 2 cm was also
recommended [97- 100]. A length of artery nearer to 3 cm probably allows for post fixation
shrinkage [99]. Whether bilateral biopsies should be performed depends on the rate of
discordance, which in a pooled analysis of four studies looking at 439 synchronous bilateral
biopsies was 5.9% [93], although the range in individual studies was 1.4% to 12.7% (101).
If the selected artery is negative for arteritis, some investigators [29, 88] advocate biopsy of
the temporal artery on the contralateral side while others [12] consider the additional burden
on the patient not justified for the small increase in diagnostic yield particularly if an adequate
length of unilateral specimen can be ascertained and reviewed by an experienced pathologist

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