Leukaemic Involvement of Bone

I must consider leukaemia because acute lymphoblastic leukaemia, the commonest childhood malignancy, frequently involves the marrow and bone and a significant minority of children present with musculoskeletal symptoms such as bone or joint pain, a limp or an arthritis, and in some this is the first or only feature before any obvious haematological abnormality. As a result leukaemia is a classic mimic that is repeatedly misdiagnosed as juvenile idiopathic arthritis, septic arthritis, osteomyelitis or chronic recurrent multifocal osteomyelitis, and the diagnosis is delayed. I would look for red flags: bone pain that is severe, nocturnal or disproportionate to the examination, pain that is metaphyseal rather than localising to a joint, systemic features such as fever, weight loss, fatigue and pallor, and hepatosplenomegaly or lymphadenopathy. The key investigation is a full blood count and blood film looking for cytopenias, particularly involvement of more than one cell line such as anaemia with thrombocytopenia, and circulating blasts, supported by a raised LDH and urate and an ESR out of proportion. Radiographs may show leukaemic lines, which are transverse metaphyseal lucent bands, with osteopenia and permeative lesions, and MRI shows diffuse marrow replacement. The diagnosis is confirmed on bone marrow aspirate and biopsy showing blasts. Crucially I would not wash out a presumed septic joint or biopsy a presumed bone tumour without first checking the blood count and considering leukaemia, and a normal initial film does not exclude it, so persistent red-flag symptoms warrant marrow examination and referral to paediatric haematology-oncology.

The radiographic features of leukaemic bone involvement are characteristic but non-specific. The classic sign in children is leukaemic lines, which are transverse radiolucent bands in the metaphyses, and there may also be diffuse osteopenia, permeative or moth-eaten lytic lesions, periosteal reaction, frank osteolytic lesions, and sometimes vertebral compression fractures. MRI shows diffuse low signal in the marrow from blast replacement, and FDG-PET shows multiple bone foci or systemic marrow uptake. None of these is diagnostic on its own, so the diagnosis is made on the blood film and bone marrow. The orthopaedic surgeon's role is principally one of recognition and referral: to suspect leukaemia in a child with unexplained bone or joint pain and red flags, to check a full blood count and film, and to refer promptly to paediatric haematology-oncology, since treatment is chemotherapy-led. The surgeon must avoid inappropriate surgery, such as washing out a presumed septic joint or biopsying a presumed primary bone tumour, without first excluding leukaemia, because that delays diagnosis and adds morbidity; if a biopsy is done, samples must go to haematopathology. The surgeon also manages skeletal complications such as pathological fractures and the late steroid-induced osteonecrosis, particularly of the femoral head, that complicates ALL treatment, and stays alert to a focal myeloid sarcoma or chloroma in myeloid leukaemia.