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]

Question 2 (10 marks)

A twelve-year-old girl of East Asian ancestry develops a flaccid paraplegia with a T6 sensory level and urinary retention over three days, preceded by a viral illness two weeks earlier. The emergency MRI shows an intramedullary T2-hyperintense, enhancing spinal-cord lesion spanning six vertebral segments, with no compressive mass. [3]

(a) Apply the Transverse Myelitis Consortium Working Group 2002 diagnostic criteria for idiopathic acute transverse myelitis, naming the progression-to-nadir window. (3 marks) [1]

(b) Explain what the lesion length (six segments) raises diagnostically, name the two antibody tests that resolve it, and state the cardinal safety rule that governs long-term drug choice. (4 marks) [3] [5]

(c) Give the first-line acute treatment with the drug, the dose, and the duration, and state how and when to escalate. (3 marks) [1] [3]

Model answer

The Transverse Myelitis Consortium 2002 criteria require: sensory, motor, or autonomic dysfunction attributable to the spinal cord; bilateral signs or symptoms (not necessarily symmetric); a clearly defined sensory level; exclusion of an extra-axial compressive cause on neuroimaging (MRI); demonstration of inflammation within the cord (a cerebrospinal-fluid pleocytosis, an elevated immunoglobulin-G index, or gadolinium enhancement on MRI, repeated at two to seven days if initially absent); and progression to the nadir between four hours and twenty-one days from the onset of symptoms. This child's bilateral paraplegia with a T6 sensory level, the exclusion of a compressive mass on MRI, and the gadolinium enhancement satisfy several of these; the lumbar puncture confirms the inflammation. [1]

A lesion spanning three or more vertebral segments is a longitudinally extensive transverse myelitis, which raises neuromyelitis optica spectrum disorder (aquaporin-4 IgG positive) and myelin-oligodendrocyte-glycoprotein antibody-associated disease (MOG-IgG positive) over multiple sclerosis, which is typically short (one to two segments), peripheral, and focal. The two antibody tests that resolve it are the serum aquaporin-4 IgG and the serum myelin-oligodendrocyte-glycoprotein IgG, both by a live cell-based assay. The cardinal safety rule is that a multiple-sclerosis disease-modifying therapy must never be started before the aquaporin-4 and MOG antibody status is known, because several of those drugs worsen AQP4-IgG-positive neuromyelitis optica spectrum disorder. [3] [5]

The first-line acute treatment is high-dose intravenous methylprednisolone at 20 to 30 mg per kg per day to a maximum of 1 g per day, given over three to five days, followed by a short oral prednisolone taper. If the deficit has not improved after forty-eight to seventy-two hours of corticosteroids (steroid-refractory disease), the escalation is to intravenous immunoglobulin at a total dose of 2 g per kg or to plasma exchange (five to seven exchanges on alternate days), not a repeat steroid course; plasma exchange is favoured early for the severe aquaporin-4-positive attack because it removes the pathogenic antibody directly. [1] [3]