Beyond Joint Pain: When Arthritis is a Harbinger of Leukaemia

Acute lymphoblastic leukaemia (ALL) can present atypically, mimicking rheumatic conditions and causing significant diagnostic delays. This case details a 12-year-old boy initially diagnosed with juvenile idiopathic arthritis (JIA) due to persistent right shoulder and elbow pain and swelling, despite normal initial blood work. Initial evaluation, including physical examination, blood tests (normal complete blood count [CBC], elevated erythrocyte sedimentation rate/C-reactive protein [ESR/CRP]), and even rheumatoid factor positivity, pointed towards JIA. However, escalating nocturnal pain unresponsive to treatment, persistently high acute phase reactants, and bone oedema on magnetic resonance imaging (MRI) ultimately triggered a bone marrow aspiration, revealing a diagnosis of precursor B-cell ALL. This case emphasises the crucial need for high clinical suspicion and thorough investigation, including bone marrow examination, when children present with atypical or treatment-resistant musculoskeletal pain, particularly with features like worsening night pain and bone oedema on imaging, to avoid detrimental delays in diagnosing life-threatening conditions like ALL.