Is Perls Prussian Blue Stain For Hemosiderin A Useful Adjunct In The Diagnosis Of Vasculitic Neuropathies?

Background: Perls Prussian blue stain (PPB) for hemosiderin, a marker of vascular injury is often employed as an adjunct in the diagnosis of vasculitic neuropathies. However, inflammation/vascular injury is also seen in leprosy, immune mediated, paraproteinemic, diabetic neuropathies, etc. The frequency of detection of hemosiderin in these neuropathies and its utility in diagnosis of vasculitis has not been explored.Objective: We evaluated 208 peripheral nerve biopsies for hemosiderin deposits by PPB stain in vasculitis (78) and compared with inflammatory/immune neuropathies [leprous neuritis-32, chronic inflammatory demyelinating polyneuropathy (CIDP)-15, paraproteinemic neuropathies (POEMS)-12, diabetic neuropathy-37] and nonimmune neuropathies [Charcot-Marie-Tooth (CMT) disease-15, vitamin B12 deficiency-7, and ischemic neuropathy in aged-12)].Results: Hemosiderin deposits were most frequent in vasculitis (48.72%) [59.2% in systemic; 43.1% in nonsystemic vasculitides] and enhanced the sensitivity of diagnosis in "probable" vasculitis (34.48%) that lacked transmural inflammation. Hemosiderin was also detected in infectious/immune-mediated neuropathies (leprous neuritis-56%, POEMS-33.3%, diabetes-18.9%) but absent in CMT, B12 deficiency, and ischemic neuropathy. Hemosiderin deposits involved epineurium in vasculitis, compared to endoneurial/perineurial location in leprosy and perineurial in POEMS and diabetic neuropathy. The sensitivity of detection was high in vasculitic neuropathy (49.35%) compared to other inflammatory neuropathies (22.3%) (P < 0.05) with high specificity (77.69% [positive predictive value (PPV)-56.71%; negative predictive value (NPV)-71.6%]. The specificity increased to 89% if leprous neuropathy was excluded, with PPV-77.5% while NPV dropped to 68.5%.Conclusion: These findings suggest that PPB stain for detection of hemosiderin is a useful adjunct in diagnosis of vasculitic neuropathy with high specificity but low sensitivity.