Cutaneous and systemic plasmacytosis vs. cutaneous plasmacytic castleman disease: review and speculations about pathogenesis.

Cutaneous and systemic plasmacytosis (C/SP), human herpes virus-8 (HHV8), negative multicentric plasmacytic Castleman disease (MPCD), and idiopathic plasmacytic lymphadenopathy are polyclonal plasma cell proliferations of unknown etiology that predominantly affect Asian individuals. Herein, we present our experience with a Vietnamese man with typical C/SP limited to the skin but, after 10 years, may have developed perirenal involvement, and with a white man with human immunodeficiency virus and HHV8 negative MPCD with involvement of skin, lymph nodes, and kidneys at presentation, and who later succumbed to gastric carcinoma. Based on a review of the literature, we suggest that C/SP, cutaneous MPCD, and idiopathic plasmacytic lymphadenopathy with skin involvement are part of a continuum rather than distinct entities and, as such, may be regarded as variants of HHV8-negative MPCD. Although the majority of patients with C/SP run a chronic benign course, special attention should be given to monitoring for pulmonary and renal involvement. We hypothesize that long-lived plasma cells originate and survive in the environment of the skin akin to other stromal "survival" niches due to the local production of interleukin 6 and that such patients might respond to agents that interfere with interleukin-6 activity.