Solitary plasmacytoma of bone and extramedullary plasmacytoma: two different entities?

The objective of this study was to evaluate the similarities between solitary plasmacytoma of bone (SPB) and extramedullary plasmacytoma (EP).

The clinical features, treatment and survival of 54 patients with localized plasmacytoma (LP) 1990 were carefully reviewed. Follow-up was expected to continue until June 1993.

Thirty-two patients were classified as having SPB and 22 EP. Most of the patients were males. particularly those in the SPB group. Their median age at diagnosis was 54 years and no significant difference between the two groups was observed. SPB occurred most frequently in the vertebral column (42%) and EP in the upper respiratory tract (73%). Fifteen patients with SPB and 2 with EP had paraproteinemia at diagnosis, multiple myeloma (MM) became evident in 75% of the patients with persistent paraprotein after therapy, and in only 22% of those in whom it disappeared. Four patients in the SPB group had immunoparesis, and 3 developed MM. Disease progression toward MM was significantly different (p=0.003) in the two groups, while overall survival differences were not significant (p=0.07) unless unrelated causes were excluded (p=0.02). Adjuvant chemotherapy did not seem to limit diffusion of the disease.

Although EP and SPB are both localized forms of plasma cell dyscrasias, SPB seems to have a greater tendency to progression MM. It appears, however, that the apparent stronger propensity of SPB to progress is actually due to the great number of cases that at diagnosis conceal an occult MM.