Child With Difficulty in Walking

A 4-year-old boy with a history of autism presents to his pediatrician's office with a complaint of right leg pain. He is presumed to have pulled a muscle; an elastic bandage is applied and he is given ibuprofen(Drug information on ibuprofen). Over the next few days, he begins falling and tripping and is unable to maintain his balance. At a return visit, the patient's mother says her son's right leg is "like Jell-O" and that he appears to be dragging the leg. He has not had a fever, but his appetite has been decreased and he has been less active than usual. He denies bowel or bladder symptoms and any history of trauma.

HISTORY

The patient has mild motor and speech delay associated with his autism diagnosis. He was hospitalized as an infant for rotavirus infection but has otherwise been healthy. He had a viral upper respiratory tract infection 2 weeks earlier and received his age 4 immunizations at around the same time. There is no family history of any neurological or muscle disorders. The child lives with his mother, father, 2 sisters, and twin brother, all of whom are healthy. He takes no medications and has had no known abnormal ingestions.

PHYSICAL EXAMINATION

The child is in no apparent distress; he is cooperative and answers questions appropriately. His weight is 20.5 kg (75th percentile); height, 112 cm (75th percentile). Temperature is 36.6°C (98.0°F); heart rate, 118 beats per minute; respiration rate, 28 breaths per minute; and blood pressure, initially 128/65 mm Hg but on a second measurement, 107/61. He is normocephalic, with clear conjunctivae and normal findings on a funduscopic examination. Lungs are clear, heart is normal, abdomen is benign. Examination of the extremities reveals no rashes or deformities and no swelling or erythema of the joints. A neurological examination shows normal strength in the left lower extremity but decreased strength in the right foot. Deep tendon reflexes in the right lower extremity are absent. The patient has a waddling gait and appears to drag his right foot. Truncal stability is normal. Sensation is normal throughout. Cranial nerves II through XII are intact.

LABORATORY AND IMAGING RESULTS

A complete blood cell count and metabolic panel are normal. Erythrocyte sedimentation rate is 15 mm/h; C-reactive protein level is less than 0.5 mg/dL. A series of radiographs of the right foot and ankle, bilateral hip and pelvis films, and a head CT scan are all normal.

Because of the constellation of symptoms and physical findings, an MRI of the cervical, thoracic, and lumbar spine is obtained, which is as shown.

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