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Washington University Experience | MISCELLANEOUS | Idiopathic Hypertrophic Pachymeningitis (IgG4 Disease) | 7G Case 7 Denouement
Not shown: The part B specimen additionally shows fragments of cerebral cortex and subcortical white matter underlying leptomeningeal inflammation. The cerebral cortex shows robust reactive changes, including reactive astrocytosis, subpial gliosis, microglial activation, and reactive endothelial atypia. Focally, small cortical vessels show evidence of vasculitis, with mixed chronic inflammatory cells surrounding and obscuring vessel lumens. Immunohistochemical and histochemical stains were performed (AFB, Fite, Gram, and GMS) without finding fungi, bacteria or mycobacteria. ---- Comment: The collective findings are consistent with dura mater and leptomeninges with necrotizing granulomatous inflammation, small vessel vasculitis, and increased IgG4+ plasma cells. We noted the patient's markedly elevated anti-PR3 antibody and normal serum IgG4. While infectious etiologies could produce the histopathologic findings which were seen here, we did not see any evidence of organisms, and many infections had been ruled out by the clinical team. The histologic findings are mostly in keeping with a diagnosis of granulomatosis with polyangiitis (GPA), namely necrotizing granulomatous inflammation with multinucleated giant cells and small vessel vasculitis involving the meninges (both pachymeninges and leptomeninges). However, the presence of abundant IgG4+ plasma cells (85 per single HPF, and IgG4:IgG ratio of nearly 30%) raises the possibility of an anti-neutrophil cytoplasmic antibody-associated vasculitis and IgG4-related disease “overlap syndrome” (Danlos et al. PMID: 28780079).
