Page 192 - The Vasculitides, Volume 1: General Considerations and Systemic Vasculitis

168 Lindsay Lally and Stephen A. Paget

and neck make it surprisingly difficult or impossible to identify the classical pathological
features of GPA in some patients [32]. By comparison, renal biopsy in patients with GPA
showed varying degrees of segmental necrotizing glomerulonephritis in 80% of tissue [32].
In the absence of renal involvement, targeted biopsy of radiographically abnormal lung
parenchyma via a thoracoscopic or open lung biopsy technique showed granulomatous
changes in 22% and capillaritis in 31% of those so studied [32] compared to the efficacy of
transbronchial biopsy in establishing the diagnosis of pulmonary vasculitis in 10% of
suspected tissues [33].

Polyarteritis Nodosa

The finding of focal, segmental necrotizing vasculitis in medium-sized arteries can
confirm the diagnosis of PAN in suspected patients. Angiographic demonstration of
microaneurysm formation is an acceptable surrogate to the histopathologic confirmation when
tissue cannot be readily obtained [34]. Histologically-proven PAN was ascertained in 70% of
patients by nerve, muscle or skin tissue biopsy in one large cohort [6]. Of 129 patients
underwent nerve biopsy including 108 with peripheral neuropathy and 21 without peripheral
neuropathy, vasculitic lesions were noted respectively in 83% and 81% of patients compared
to muscle biopsy which showed vasculitis respectively in 68% and 60%. Angiography
showed renal and gastrointestinal microaneurysms or stenosis respectively in 66% and 57%
of patients. While PAN frequently involves the gastrointestinal tract especially the small
intestine, biopsy of visually apparent lesions on luminal exam rarely provide histopathologic
confirmation of vasculitis [35]. Renal biopsy may be negative even in patients with frank
organ involvement due to sampling error. Unlike AAV, where the histopathologic renal lesion
is the kidney glomerulus, microaneurysm formation due to PAN increases the risk of bleeding
associated with renal biopsy.

Giant Cell Arteritis

Histopathologic evidence of vascular wall infiltration by giant cells at the junction of the
intima and media, leading to thrombosis, intimal hyperplasia, and fibrosis [36] is the gold
standard method of GCA diagnosis. Accordingly, temporal artery biopsy is recommended for
all patients with suspected GCA [37]. The sensitivity of temporal artery biopsy in GCA has
been estimated to be 85% [38]. Evidence in support of unilateral as compared to bilateral
temporal artery biopsy is lacking, leaving it up to the judgment of the treating physician.
Temporal artery ultrasonography can be used to guide the surgeon to the arterial segment with
the clearest halo sign in performance of temporal artery biopsy [31], however the
discontinuous nature of inflammation in GCA leading to skip lesions may still lead to
unforeseen false-negative results when the tissue specimen is of insufficient length and
multiple sections are not examined. Certain clinical features, such as the presence of jaw
claudication can increase the positivity predictive value of a temporal artery biopsy.

Arteritis can be observed histologically even after several weeks of high dose
corticosteroid therapy [39]. Notwithstanding, the heightened risk of ischemic complications
culminating in irreversible visual loss in early untreated GCA has led to the recommendations

Complimentary Contributor Copy