Clinical information:  The patient was a 9 year-old African-American boy. He developed left lower extremity progressive weakness 4 months ago (in May). As per his father, the patient started "dragging" his left leg in May. He was first evaluated by the orthropedic service and was later referred to the neurosurgery service of this institution. The patient had asthma and his treatment had been intermittent.  There was no history of seizures or other neurologic disease. The family history was unremarkable. He was born in the United States and never traveled beyond the state border of Oklahoma.

    On physical examination, the patient was awake, alert, and well oriented to time, place , person, and situation. There was no memory or f language impairment or mental retardation. Strength in both upper extremities were 5/5 bilaterally. There was also a 5/5 strength in extension and flexion on the right lower extremity. His strength for left hip flexion, extension, abduction and adduction was 5/5. In his left knee, the strength for extension was 5/5 and flexion was 4/5. Strength on left ankle dorsiflexion was 4/5,  planter flexion was 2/5, inversion and eversion were 5/5. His peripheral sensation was intact. The reflexes were increased to 3/4 in lower extremities with ankle clonus on the left. There were also bilateral upgoing toes. There is no impairment on sphincter functions. There was not history or skin rash or insect bite. The remaining of the physical examination was unremarkable. An MRI followed by a biopsy were performed. The representative images are illustrated below:

A. T1	B. T1+Contrast	C. T1+Contrast	D. T2	E. T1+Contrast	F. Squash
G. Squash	H. Frozen	I. Frozen	J. Frozen	K.	L.
M.	N.	O.	P. NFP	Q. LFB-PAS

What is your diagnosis? Discussion