The Cause of Dissociated Motor Loss in the Upper Extremity with Cervical Spondylosis

Abstract

The cause of a t r o p h i c motor loss in the u p p e r e x t r e m i t y in cervical spondylosis has been difficult to i n t e r p r e t because of its c o m m o n association with spinal cord s y m p t o m s and the relative absence of sensory loss. There has been a t e n d e n c y to a t t r i b u t e this dissociated m o t o r loss to cystic degeneration in the anterior horns of the cord. However, some cases with extensive u p p e r ext r e m i t y paralysis do n o t present any long t r a c t spinal cord s y m p t o m s . Because of these, the causative p a t h o l o g y has remained in doubt. We recently h a v e h a d t h e opportunity to follow such a case to p o s t m o r t e m examination, where it became clear t h a t the dissociated m o t o r loss was due to i n d e p e n d e n t compression of the m o t o r roots intradurally, not to cord pathology. This s t u d y clarifies some misconceptions concerning this s y n d r o m e a n d seemed worthy of report.

Cervical spondylotic amyotrophy

“…Whether the pathogenesis of this syndrome is selective damage to the ventral root or to anterior horn is still controversial. On the basis of findings in an autopsy performed in one patient associated with cervical spondylotic amyotrophy, Keegan [25] demonstrated that selective ventral motor root lesions are the cause in the pathogenesis of cervical spondylotic amyotrophy. The autoptic finding that Luschka joints significantly contribute to this anterior root impingement supports this mechanism [33].…”

“…The proximal-type patients have muscular atrophy in the C5 and C6 myotomes [3,19,22,25,30,38], whereas patients with the distal-type amyotrophy have muscular atrophy in C7, C8, and Th1, with muscular atrophy distributed to the forearm and intrinsic muscles. In one study of 16 proximal-type patients and 15 distal-type patients, the distal-type patients often presented cold paresis and/or postural finger tremor, and none of distal-type patients had extension of atrophy to the proximal muscles during a long course of their illness.…”

“…In 1952, Brain et al [7] first reported cases of cervical spondylosis with muscle atrophy of the upper extremities without sensory disturbance or pyramidal signs. The dissociated motor loss syndrome in cervical spondylosis was reported by Keegan [25], and the etiology of this syndrome was thought to be selective damage by bony spurs of the motor roots. In 1975, Sobue et al [39] concluded that such condition was caused by segmental myelopathy and advocated nominating this condition as cervical spondylotic amyotrophy.…”

Cervical amyotrophy caused by hypertrophy of the posterior longitudinal ligament

“…6,7,12 In the present case, an intramedullary high-signal intensity lesion appeared in the central gray matter to the anterior horn of the compressed cord on transverse T2-weighted MRI. Such intramedullary high-signal intensity lesions are referred to as`snake-eyes appearance 10 or fried-egg appearance 13 , and are thought to be irreversible necrosis, rather than reversible edema.…”

“…6,11,16 Therefore, the muscular atrophy of the present case might have been caused by multisegmental damage of the anterior horns due to HPLL, unlike the theory of damage of the ventral nerve roots proposed by Keegan. 7 Wada et al 15 documented that single-segment injury of the anterior horn cells would not be su cient to develop muscular atrophy. We thus consider HPLL from C4 to C6 to have been the major factor in the muscular atrophy of this patient.…”