Metaplastic Ossification of the Temporal Artery with Osteoclast-Like Giant Cells: A Mimicker of Giant Cell (Temporal) Arteritis

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Abstract
Purpose: To describe a patient presenting with suspected giant cell (temporal) arteritis (GCA) in whom subsequent temporal artery biopsy showed luminal narrowing by medial calcification, metaplastic ossification, and fibrointimal proliferation, consistent with calciphylaxis. Methods: A 55-year-old man with end-stage renal disease presented with unilateral loss of vision and elevated erythrocyte sedimentation rate and was initially treated as though he had GCA; however, a subsequent temporal artery biopsy showed marked luminal narrowing by medial calcification, metaplastic ossification, and fibrointimal proliferation, consistent with calciphylaxis. In addition, the tunica media of the affected artery contained multinucleate giant cells, but these represented osteoclasts and foreign body giant cells reacting to calcium, rather than a part of GCA. Results: This is a rare report of metaplastic ossification and the finding of non-GCA-related giant cells in the tunica media of the temporal artery, thus representing a clinical and histopathologic mimicker of GCA. Conclusions: The clinical differential diagnosis of GCA includes other etiologies that can present similarly; however, temporal artery biopsy can discern the underlying pathology. Importantly, the identification of giant cells is not required for the diagnosis of GCA, and likewise, as our case shows, the finding of giant cells in the wall of a temporal artery does not always imply a diagnosis of GCA.

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