Spinal cord compression and transverse myelitis — formative SAQs

Question 1 (10 marks)

A previously well nine-year-old boy presents with three days of thoracic back pain that wakes him at night and is worse lying flat. This morning he developed a weak left leg and could not pass urine. On examination he has a sensory level at T10, a flaccid left leg with reduced reflexes, and a palpable distended bladder. He is afebrile. [6]

(a) State the single most important investigation, the urgency with which it must be performed, and why it is not delayed for bloods or a lumbar puncture. (3 marks) [1] [6]

(b) If the investigation shows an extradural mass with vertebral body destruction, name the most likely diagnosis in this age group, give two further paediatric malignancies in the differential, and state the immediate medical treatment with the principle of its dosing in a child. (4 marks) [6] [7]

(c) Describe the timing and rationale for definitive treatment, and state the single strongest predictor of his eventual motor outcome. (3 marks) [6]

Model answer

The single most important investigation is an emergency whole-spine MRI with gadolinium, performed within hours and never delayed for bloods or a lumbar puncture. It is the rate-limiting step because it 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. A lumbar puncture is performed only after a compressive lesion is excluded, because puncture below a complete cord block risks neurological deterioration. [1]

An extradural mass with vertebral body destruction in a previously well child makes a malignant spinal cord compression the most likely diagnosis. Two further paediatric malignancies in the differential are non-Hodgkin lymphoma and leukaemia presenting as a chloroma (other acceptable answers include Ewing sarcoma, rhabdomyosarcoma, neuroblastoma, and germ-cell tumour). The immediate medical treatment is dexamethasone started at once to reduce cord oedema and preserve neurological function; in children the dose is weight-based and set by the local paediatric-oncology and neurosurgery protocol, with the adult National Institute for Health and Care Excellence benchmark of a 16 mg loading dose followed by 16 mg per day in divided doses, continued until definitive treatment and then tapered. [6] [7]

The definitive treatment is surgical decompression (plus tumour resection) timed within twenty-four to forty-eight hours of the loss of ambulation, with urgent radiotherapy or chemotherapy for a radiosensitive or chemosensitive tumour. The rationale is the compressive cascade: an extradural mass first causes venous congestion and cord oedema (a reversible phase), then ischaemia, then irreversible cord infarction, so the decompression is timed to occur within the salvageable window. The single strongest predictor of his eventual motor outcome is his ambulatory status at presentation - a child still walking on arrival is likely to remain walking, while a child who arrives paraplegic rarely recovers. [6]