A case of Mollitias and Fragilitas Ossium – unusual presentation of hairy cell leukaemia followed by the diagnosis of nonsecretory myeloma

Summary Hairy cell leukaemia (HCL) is a B‐cell malignancy with a late developmental arrest. This report describes a patient that presented with leucocytosis and splenomegaly. The abnormal leucocytes showed typical morphology and expressed CD103, CD11c, CD19 and CD20 but not CD25 by immunophenotyping. The patient failed to respond to splenectomy and then developed lytic bone lesions and pathological fractures, which progressed despite a single course of cladribine chemotherapy. Review of the pathology of the bone reamings showed nonsecretory myeloma of the same kappa‐light chain isotype. He went on to receive induction chemotherapy in preparation for an autologous stem‐cell transplant but failed to mobilize sufficient numbers of stem cells. He has had two localized relapses with bony lesions, one within 6 weeks of stopping chemotherapy for which he received localized radiotherapy and thalidomide consolidation. Sequential myeloma has been described in HCL. There is controversy whether this represents clonal evolution or a secondary malignancy. An increased rate of secondary malignancies has been reported by some, but not other, authors in long‐term survivors of HCL. This case illustrates the value of a repeat pathological review in case of unexpected complications.