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Answers on p 570.
A 19 month old well boy presented with a week’s history of refusal to walk unsupported and favouring crawling. He had been increasingly unsteady during the preceding three weeks and appeared to be in pain during nappy changes when both legs were held flexed and abducted at the hips. There was no recent feverish illness or trauma. Bowel and bladder function was normal. His development had been age appropriate to date. He walked unsupported at 1 year of age and had been an active member in a child care group. Examination revealed symmetrically decreased deep tendon reflexes of the lower limbs with flexor plantar response. Lower limb musculature and spine looked normal. Anal tone and hip examination was normal. He pulled easily to stand and would only take a few steps across the room when supported. He crawled well with no obvious asymmetry of movements. Investigations revealed raised C reactive protein of 45 mg/l, erythrocyte sedimentation rate of 73 mm/hour, and a white cell count of 8.5 × 109/l (neutrophil count 2.98 × 109/l). Ultrasound of the hips and abdomen and a bone scan were normal. Rheumatoid and viral serological screens were negative as were all blood cultures. Plain radiography of the thoracolumbosacral region showed loss of the disc height at the L5–S1 level and loss of clarity of the adjacent end plates (fig 1). He had magnetic resonance imaging of the spine (fig 2). He was given a three week course of antibiotics (parenteral ceftriaxone and oral sodium fusidate for the first 10 days followed by oral flucloxacillin and sodium fusidate for the rest of the course). Before starting antibiotics, C reactive protein had fallen to 2.9 mg/l, lower limb reflexes were more easily elicited, and he was standing unsupported for longer periods. By the end of the course of antibiotics, the inflammatory markers had normalised and he was able to walk unsupported. More recent x rays did show that there was no significant disruption of the disc space. Repeat magnetic resonance imaging of the spine a year later is shown in fig 3.
What is the likely diagnosis and what do the magnetic resonance imaging studies (figs 2 and 3) show?
What are the alternative differential diagnoses of refusal to walk in a well afebrile toddler?