Congenital myasthenic syndromes.

Congenital myasthenic syndromes (CMS) are a heterogeneous group of uncommon, inherited disorders affecting the neuromuscular junction. The defects interfere with presynaptic, synaptic, or postsynaptic function and compromise neuromuscular transmission. Most patients with CMS have similar clinical features regardless of the underlying defect, but attention to clinical and electrodiagnostic parameters can narrow the diagnostic spectrum. Recent advances in our understanding of the cellular mechanisms underlying specific syndromes allow DNA testing for some forms of CMS. Diagnosis of CMS enables a rationale for management to be developed. Two cases of genetically determined CMS as well as an undiagnosed infant are presented to highlight the clinical and electrophysiological difficulties associated with the diagnosis and management of such syndromes.

Delayed vestibular evoked responses to the eyes and neck in a patient with an isolated brainstem lesion.

OBJECTIVE: Two recently described tests of the vestibular system, vestibular evoked myogenic potentials (VEMPs) and ocular vestibular evoked myogenic potentials (OVEMPs), test the descending and ascending vestibular brainstem pathways, respectively. We describe a case of a patient in whom these investigations localised the lesion and suggested its nature. METHODS: VEMPs (to clicks and short duration galvanic stimulation) and OVEMPs (to clicks) were recorded. RESULTS: Click- and galvanic-evoked VEMPs were delayed on the left side (by approximately 5-6 ms), and click-evoked OVEMPs were similarly delayed (by approximately 4 ms) following left-sided stimulation. Repeat testing 21 months later showed partial resolution. CONCLUSIONS: The observed delays in evoked potentials suggested a demyelinating lesion. Furthermore, the similarity in delayed responses to neck and extraocular muscles was suggestive of a lesion at the root entry zone of the vestibulocochlear nerve. SIGNIFICANCE: VEMPs and OVEMPS may thus provide information about the location and nature of lesions affecting central vestibular pathways.

Focal and generalized peripheral nerve dysfunction in spinal cord-injured patients.

SUMMARY: The present study was undertaken to quantitate the incidence and clinical patterns of peripheral nerve dysfunction distal to the level of injury in patients with spinal cord injury (SCI). Through retrospective analysis, SCI patients were identified after referral for neurophysiologic investigation of new neuropathic symptoms. In total, peripheral nerve or nerve root lesions developed in 34 SCI patients, most commonly within the first year after SCI. Carpal tunnel syndrome was the most common upper-limb neuropathy (34%); sciatic neuropathy was the most common lower-limb abnormality (8.5%). A significant proportion of SCI patients had neurophysiological evidence of generalized peripheral nerve dysfunction, specifically axonal neuropathy (18%). Tetraplegic patients developed more frequent peripheral nerve lesions than paraplegics. Although most SCI patients presented within 4 years of their original injury, in a more chronic population of SCI patients that developed neuropathy 5 years after injury, 60% had evidence of coexistent syrinx formation. Maintenance of peripheral nerve function is a critical issue in all acute SCI and rehabilitation units, particularly in the context of spinal cord neuronal regeneration projects.