Cervical Spondylotic Amyotrophy

Keegan (1965) reported a patient who presented with dissociated motor loss, an acute paralysis of the upper extremity with minimal sensory signs and no long tract signs, and documented an anterior root lesion following autopsy. Sobue et al. (1975) reported similar cases using the term cervical spondylotic amyotrophy (CSA), but postulated pathology of the anterior horn. Although Keegan's dissociated motor loss surely referred to isolated motor paresis with no or minimal sensory signs, contrary to existing criticism, a more general term, CSA, should be preferred. CSA is divided into proximal and distal types. Distal CSA often presents with a drop finger, and thus may be misdiagnosed as posterior interosseous nerve palsy. Documentation of the involvement of ulnar muscles by clinical signs and EMG would lead to the diagnosis of distal CSA. Proximal CSA may be confused with neuralgic amyotrophy (NA), although the sparing of the serratus anterior and the stereotypic involvement of deltoid, infraspinatus, biceps brachii, and brachioradialis suggest CSA. Cervical MRI is not diagnostic in around half of CSA cases, and denervation in paraspinal EMG is a more sensitive test that can exclude NA. Amyotrophic lateral sclerosis is another important differential diagnosis for CSA.