Spinal cord compression and transverse myelitis — branching viva

Opening branch — the nine-year-old with nocturnal back pain and a weak leg

A previously well nine-year-old presents with three days of thoracic back pain that wakes him at night and is worse lying flat, then a weak left leg and acute urinary retention, with a T10 sensory level. The candidate must first state that the single most important next investigation is an emergency whole-spine MRI with gadolinium, performed within hours and never delayed for bloods or a lumbar puncture. The teaching point is that the MRI - not the history and not the bloods - resolves the fork between a compressive structural lesion, a surgical emergency needing dexamethasone and decompression, and an inflammatory transverse myelitis, a medical emergency needing methylprednisolone. ^{[1] [4]}

The examiner probes the symptom sequence and the urgency. The candidate describes the classic order of a compressive lesion - back pain, then radicular pain, then motor weakness, then a sensory level, then sphincter loss - and notes that nocturnal back pain worse lying flat, with a sensory level and urinary retention, is an established lesion with a narrow salvage window. The candidate states that ambulation at presentation is the single strongest predictor of outcome, and that the surgical decompression is timed within twenty-four to forty-eight hours of the loss of ambulation because the cord converts from a reversible oedematous phase to irreversible infarction within that window. ^[4]