Abstract
[Objective] To report our experience on correlation between surgical outcomes for proximal-type cervical spondylotic amyotrophy (CSA) resulting from unilateral ventral nerve root (VNR) involvement and compound muscle action potentials (CMAPs) of the deltoid and the biceps brachii muscles recorded preoperatively.
[Methods] We retrospectively studied 10 proximal-type CSA patients who underwent surgical treatment of the cervical spine and preoperative CMAP recording from the deltoid and biceps after Erb-point stimulation. The central motor conduction time calculated based on the motor evoked potentials from the abductor digiti minimi after transcranial magnetic stimulation and the F waves excluded the corticospinal tract involvement. The deltoid and biceps CMAPs on the normal side also excluded a possibility of the anterior horn involvement. Postoperative improvement in muscle strength of more than 2 MMT grades or complete recovery was classified as excellent, 1 MMT grade of recovery as good, and no improvement as fair.
[Results] The improvement was graded as excellent in 7 cases, good in 0, and fair in 3. Of the 7 patients graded as excellent, 5 showed the average of CMAP amplitudes for the deltoid and biceps of 30 to 50% on the affected side compared to the normal side, and the remaining 2 patients 10 to 30% on the affected side compared to the normal side. All three patients graded as fair showed the value of 10 to 30%.
[Discussion] The average of deltoid and biceps CMAP amplitudes of less than 30% on the affected side, as compared with the normal side, indicated severe involvement of VNR. Although decompression surgeries for proximal-type CSA, if caused by unilateral VNR involvement, tend to be effective, we must recognize that this is not the case with the severe involvement of VNR as predicted by the deltoid and biceps CMAP of low amplitude.
[Conclusions] In proximal-type CSA with unilateral VNR involvement, the average of side-to-side amplitude ratios of the deltoid and biceps CMAPs recorded preoperatively correlated with postoperative functional recovery. Surgical intervention to the cervical spine in this disorder produces excellent results in patients with the amplitude ratio of 30 to 50%, but this is not always the case in patients with the ratio of less than 30%.
