Hairy cell leukaemia variant with periarticular joint infiltration and excellent radiotherapy response.

Hairy cell leukaemia (HCL) is rare, accounting for only 2% of leukaemias. An even more infrequent variant has been described, HCL-V. The clinicopathologic features of these two entities overlap significantly, although they differ in a number of aspects, including demographics and immunophenotype. In this report, we present the case of a man with HCL-V diagnosed 12 years previously, who is currently haematologically stable with an unusual complication of joint pain due to extensive bony expansion secondary to leukaemic infiltration, and atypical skeletal imaging. His painful joint disease responded dramatically to radiotherapy.