MR Imaging of the cervical cord in juvenile amyotrophy of distal upper extremity.

We report the MR studies of the cervical cord in seven patients presenting juvenile muscular atrophy of distal upper extremity. This illness, also known as monomelic amyotrophy or benign focal amyotrophy, is distinct from the other motor neuron diseases. Seen in young males, it is characterized by muscular atrophy of the hand, and usually of the forearm, most often unilateral. The underlying process, of unknown origin, affects the anterior horn cells in the lower cervical cord. The gradual onset of purely motor disturbances may mimic early amyotrophic lateral sclerosis. This latter diagnosis may be excluded because of clinical stabilization and lack of pyramidal tract involvement. In our series, five MR studies were positive. In three cases we were able to demonstrate focal and unilateral atrophy in the lower cervical cord limited to the anterior horn region. Morphologic MR findings correlated with clinical and electromyographic features. In two other cases the MR-clinical correlation was more complex. No pathologic MR signal was detected on either T1- or T2-weighted images. Although the diagnosis of monomelic muscular atrophy is based on neurologic and neurophysiologic data, MR provides confirmatory evidence as well as useful information contributing to an understanding of this disease.