WEAK LEGS
History
Archie is an 18-month-old boy who is referred by his GP to the paediatric day unit with a 1-week history of reduced mobility, worse in the previous 24 hours. His parents assumed he had had a minor injury at nursery because he has also been complaining that his back is sore, although there have been no witnessed events. The GP initially wondered about a reactive arthropathy affecting his hips because Archie also has a cold, but has sent him in because of the deterioration. Looking back, his parents think he has been a bit unsteady for a couple of months but this has been attributed to an ear infection. Archie walked confidently from 11 months and the rest of his development is normal. There is no significant past medical history or family history.
Examination
Archie is a generally healthy boy but is in some discomfort. Observing him in the playroom he needs propping up to sit and keeps his back very still and straight when he tries to move or reach for objects. There is very little spontaneous movement in either leg, worse with the left than the right, and he cannot weight-bear, crawl or pull himself to stand. He is reluctant to be examined but his cranial nerves and arms appear normal. Passive movement of his legs is normal, with a full range of movement in his joints. However, tone and power are reduced in both legs and reflexes are absent on the left and reduced on the right. There is no back tenderness. Examination of his cardiovascular and respiratory systems is normal. In his abdomen, there is a smooth, non-tender mass in the suprapubic region that appears to be arising out of the pelvis. It is dull to percussion.
INVESTIGATIONS
Normal
Haemoglobin 12.3 g/dL 11.5–15.5 g/dL
White cell count 8.4 109/L 6.0 17.5 109/L
Platelets 365 109/L 150–400 109/L
Sodium 138 mmol/L 138–146 mmol/L
Potassium 4.5 mmol/L 3.5–5.0 mmol/L
Urea 4.2 mmol/L 1.8–6.4 mmol/L
Creatinine 46 µmol/L 27–62 µmol/L
C-reactive protein 6 mg/L 6 mg/L
Questions
• What is the differential diagnosis of back pain in children?
• Which of these is most likely in this case?
• What should happen next?
Medicine
Unlike adults, in whom back pain is frequently mechanical or psychological in origin, back pain in children, especially pre-adolescent, is almost always pathological. It can be difficult for children to localize pain and careful observation is crucial – children with back pain tend to maintain a straight, stiff back and refuse to bend forward to pick up objects from the floor.
Differential diagnosis of back pain in children
• Developmental abnormalities – spondylolysis (defect in pars interarticularis), spondylolisthesis (spondylolysis with anterior slippage of affected vertebra), scoliosis
• Traumatic – vertebral stress fractures, muscle spasm due to overuse, e.g. in athletes and gymnasts, prolapsed intervertebral disc
• Neoplastic – primary benign or malignant vertebral or spinal cord tumours, leukaemias or lymphomas, metastases, e.g. neuroblastoma
• Infection – discitis (common before 6 years), vertebral osteomyelitis
• Rheumatological – pauciarticular juvenile rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis
Of these, only a prolapsed disc and tumours are associated with neurological abnormalities and the former is very rare, especially in young children. Hence a neoplastic cause is much the most likely. Archie has a flaccid paralysis of both legs with reduced or absent reflexes. The abdominal mass is probably his bladder which is neuropathic. No mention is made of any history of sphincter problems, but as he will still be in nappies this is difficult to assess. Parents may notice a reduction in the urinary stream in boys. His anus should be inspected and may be patulous. The parents should be asked about the presence of constipation. Detecting a sensory level at this age is extremely difficult.
The pointers to serious pathology in children with back pain include:
• persistent or worsening pain
• systemic features such as fever, malaise or weight loss
• neurological symptoms or signs
• sphincter dysfunction
• young age – especially 4 years when a tumour is most likely.
This is a medical emergency. If Archie is not to have permanent loss of sphincter control and irreversible damage to his legs, he needs urgent investigation and intervention to reduce cord compression. MRI is the investigation of choice and no time should be lost – hours can make a difference (see Fig. 70.1). He should be referred immediately to a paediatric neurosurgery centre. Spinal cord tumours are classified according to their anatomical location: intramedullary (within the cord), extramedullary intradural (usually benign) and extramedullary extradural (usually metastases). Further treatment and prognosis will depend upon the findings. This boy was found to have a diffuse intramedullary spinal tumour from T7 to T12.
He underwent limited debulking. Histology showed a low-grade pilocytic astrocytoma. Although these are slow-growing indolent tumours, it is their critical location that governs morbidity and mortality. The surgical options are limited and radiotherapy likewise. Trials of chemotherapy are in progress.
KEY POINTS
• Back pain in children should be assumed to be organic until proven otherwise.
• To minimize irreversible damage, back pain in association with neurological abnormalities is an indication for urgent MRI scanning and referral to neurosurgery.
• Location is a key predictor of outcome in brain and spinal cord tumours.
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