A 15-yr-old boy complained of a one-year history of slowly progressive weakness of the right hand and forearm, which worsened in cold weather. He also sensed intermittent fasciculations in the right-hand and forearm muscles. Besides, he suffered from coarse hand tremor, particularly when writing. Quite recently, he has noted the weakness of the other hand of a similar nature. He has been very athletic in sport activities like basketball, and has grown as much as 30 cm (1 foot) in height over the past two years. His medical history was non-contributory, and he denied any allergic disease. None of his family members reported having similar symptoms.
A neurological examination revealed that he had a bilateral atrophy of intrinsic hand muscles and forearm muscles except for the brachiradialis, and the atrophy was worse in the right hand. However, the weakness was noted only in the right hand and forearm on manual muscle testing (MRC grade IV+) including elbow extension. The other muscles, including the brachioradialis, were normovolemic and exhibited normal power, referred to as "oblique" amyotrophy. The tendon reflexes were normal with flexor plantar responses from both sides. Cranial nerve functions were normal as well. No ataxia, or sensory disturbances, or extrapyramidal signs were noted.
Motor nerve conduction studies of the right median and ulnar nerves, which were recorded at abductor pollicis brevis and abductor digitii minimi, showed normal motor nerve conduction velocities (54 and 59 msec over the segment between wrist and elbow, respectively). CMAP amplitudes were still in the normal range (5.8 and 8.4 mV, respectively) in spite of the atrophy of those recording muscles. But terminal latencies were 4.0 and 3.4 msec when normal limits were 3.6 and 2.5 m/sec, respectively; and F-wave latencies, 29.4 and 33.3 msec when normal limits of both nerves were 28 msec. The measurements in the motor nerve conduction studies of the left arm exhibited the similar features, excepting that the left arm was less affected. Sensory nerve conduction studies of the bilateral median, ulnar, medial, and lateral antebrachial cutaneous nerves showed normal conditions. Electromyography illustrated actively denervated and reinnervated patterns in the bilateral triceps brachii, pronator teres, extensor digitorum communis, first dorsal interosseus, or abductor pollicis brevis. Muscles innervated by the fifth and sixth cervical roots, such as the brachioradialis, biceps brachii, or deltoid - as well as lower extremity muscles and the tongue - showed a normal electromyographic pattern. These clinical and electrophysiological findings were suggestive of either anterior horn cell degeneration or root lesions involving the seventh and eighth cervical and first thoracic segments of the cord.
Simple cervical spine radiographs showed neither abnormalities with the exception of a loss of physiologic lordosis, nor a misalignment of the vertebral bodies in the flexed neck position (not shown). T1- and T2-weighted cervical MRI in the neutral position were unremarkable with normal contour and signal intensity of spinal cord (Fig. 1, 3A). With the neck flexion, sagittal and axial cervical MR images showed an anterior shifting of the posterior wall of the cervical dural sac below the third cervical vertebral level compressing the cervical spinal cord from the fifth cervical to the first thoracic vertebral levels (Fig. 2A). The anterior-posterior diameter of the spinal canal was reduced to about 30% of that in the neutral position. On enhancement, the widened posterior epidural space displayed a homogeneous strong enhancement with some signal flow void, suggesting a passively widened epidural venous plexus (Fig. 2B). The sixth and seventh cervical spinal segments were dynamically compressed when the patient flexed his neck forward, and the compression was more pronounced on the right side than on the left (Fig. 3B).
After confirming the compression of cervical cord on neck flexion, motor evoked potentials as well as median and posterior tibial somatosensory evoked potentials were performed both in anteflexion and in the neutral position of the neck. The results were turned out normal without a consistent latency prolongation between these two positions (central motor conduction time [CMCT] in the right abductor digitii quintii=8.1 and 8.6 msec, respectively; CMCT in the right abductor hallucis=16.9 and 16.6 m/sec, respectively).
Since the initial evaluation, two years have elapsed and no further progression has been noticed until now.