A Toddler who cannot sit

A 3-year-old boy is observed to be progressively unable to walk or sit for several days.  He has no obvious spinal tenderness, but is more irritable whilst attempting to sit. He is otherwise well with no fever, cough or choking or change of voice  (considering muscle weakness as a cause of being unable to sit). There was no history of sphincter change (considering spinal cord involvement). On examination, he appeared well and did not appear in pain. He had no obvious spinal tenderness or deformity. Neurological examination was normal. He appeared in a frog leg position and was unable to weight bear.

The most likely diagnosis is Discitis which is inflammation of the intervertebral disc. It is rare and occurs in children at around 2-5 years of age, who present with irritability, back pain, limp, or refusal to walk. Pain on nappy or diaper change can be observed. Children may refuse to bend forward or to sit, with tenderness over spine. Hip pain and stiffness and decreased power and reflexes can be seen. Most patients have had symptoms around one month before diagnosis made.

MRI spine with gadolinium can be normal initially but is diagnostic showing inflammation and helps to exclude osteomyelitis, tumours and spinal cord pathology. Muscle enzymes are normal (to exclude muscle disease as a cause of being unable to sit). Inflammatory markers (Erythrocyte sedimentation rate) are elevated in most patients. There is no need to undertake disc biopsy to diagnose children with discitis. 

Antibiotic therapy (anti-staphylococcal agents to cover the commonest organisms isolated) associates with earlier response and fewer relapses. Bed rest, analgesia and immobilisation by casting help with pain control. The prognosis is usually good but abnormal disc space and adjacent vertebrae on radiographs may occur long term.