Muscular polyarteritis nodosa as a cause of fever of undetermined origin: a case report and review of the literature.

We describe an unusual presentation of a localized form of polyarteritis nodosa (PAN) manifested by fever of undetermined origin (FUO). Biopsies of the gastrocnemius muscle revealed necrotizing arteritis and initiation of prednisolone (PSL) brought rapid response. The PAN localized to muscle is rare; furthermore, this disease presented as FUO is very rare. We want to increase awareness that muscle can be also a single-affected site as well as other well known sites such as appendix, gallbladder, uterus or testis, and skin. Since there is no single appellation for this disease, we would like to propose the term "muscular PAN".