A 14-year-old boy presented with several months of progressive low back pain. Magnetic resonance imaging showed a destructive mass of the L3 vertebra (panel A). Computed tomography revealed lytic lesions in the left sixth (panel B) and eighth ribs, T12 and S2 vertebrae, and left parasagittal calvarium (panel C). Biopsy of L3 identified sheets of cells with an eccentric nucleus and prominent Golgi apparatus (panel D, hematoxylin and eosin stain, original magnification ×40); cells were positive for CD138 and CD56 (panel E, CD138 immunostain, original magnification ×40; panel F, CD56 immunostain, original magnification ×40), and negative for CD45 expression. In situ hybridization identified κ light-chain restriction (panel G, original magnification ×40). Cytogenetic analysis was negative. Bone marrow evaluation was normal. Additional workup identified a small serum monoclonal immunoglobulin A spike of κ light-chain type (panel H, arrow). Complete blood count, calcium, lactate dehydrogenase, hepatic, and renal function laboratory results were normal. Urine protein was negative and β2-microglobulin was normal. A diagnosis of multiple myeloma was made. The patient underwent emergent radiation to the L3 lesion due to progressive neurologic symptoms followed by systemic therapy resulting in resolution of the monoclonal spike and reduction of the L3 lesion.

Multiple myeloma is uncommon in the pediatric population, and prior cases suggest a milder clinical presentation vs that of adults. Nevertheless, it is part of the differential diagnosis of destructive bony lesions and appropriate workup will uncover it.