Background: Inflammatory pseudotumor (IPT) also known as inflammatory myofibroblastic tumor (IMT) or plasma cell granuloma (PCG) has been rarely reported in the skin.
Methods: We describe five patients with cutaneous IPT and present clinicopathologic features along with detailed immunohistochemical analysis including anaplastic lymphoma kinase (ALK)-1.
Results: The patients age ranged from 15 to 89 years with a median of 56 years. All patients presented with solitary, firm, papules and nodules. There was no evidence of constitutional symptoms, local recurrence, or lymph node involvement. Histopathological examination revealed two distinct patterns; one type (n = 3) displayed dense, lymphoplasmacytoid infiltrates containing lymphoplasmacytoid cells and plasma cells with occasional germinal centers and hyalinized collagen bundles but was devoid of a myofibroblastic component. It showed features of tumors previously described as cutaneous PCG. Although an infectious etiology, including Borrelia burgdorferi-specific DNA, could not be demonstrated, we observed many features that overlapped with those of fibrous nodules of acrodermatitis chronica atrophicans. The other pattern (n = 2) revealed spindled myofibroblasts focally arranged in a fascicular pattern, an admixed lymphoplasmacytoid infiltrate set in a background of thickened collagen bundles, findings akin to the conventional type of IMT. The cases with a myofibroblastic component (n = 2) did not show any evidence of ALK-1 reactivity.
Conclusions: We believe that the term cutaneous IPT subsumes lesions of diverse etiology. Tumors with detectable myofibroblasts represent true cases of IMT. Cutaneous PCG is a discrete disorder biologically distinct from conventional IMT representing a reaction pattern that is also found in disorders, such as spirochete-induced fibroid nodules and localized chronic fibrosing vasculitis.