Familial granulovacuolar lobular myopathy with electrical myotonia

We report 3 patients with a myopathy characterized by profound selective muscle wasting and weakness, electrical myotonia without clinical myotonia and an unusual muscle biopsy. Cryostat sections showed muscle fibers with vacuoles containing hematoxylinophilic granules, and 30% of type I fibers showed demarcation of their sarcoplasm into "lobules" due apparently to reorganization of myofibrillar elements. The electrical myotonia suggests an underlying muscle membrane defect. Two of the patients are siblings suggesting that the disorder may be inherited.

F-wave conduction velocity in the central segment of the peroneal and tibial nerves

A simple method was devised to measure the F-wave conduction velocity (FWCV) in the central segment (knee to spinal cord) of the peroneal and tibial nerves in contrast to the conventional motor nerve conduction velocity (MNCV) in the distal segment (knee to ankle). In 33 normal subjects, the FWCV in the central segment (56.3 +/- 4.9 meters/sec for peroneal nerve; 54.4 +/- 3.6 meters/sec for tibial nerve) was slightly faster than the MNCV in the distal segment (49.5 +/- 3.8 meters/sec; 46.8 +/- 3.4 meters/sec) as measured in the conventional manner. In 4 of 14 patients with the Guillain-Barrĕ syndrome, the F-wave was absent or slowed in the face of normal MNCV indicating more marked slowing of nerve conduction proximally. The average FWCV (36.8 +/- 13.6 meters/sec; 42.2 +/- 9.3 meters/sec) and MNCV (41.4 +/- 8.0 meters/sec; 39.0 +/- 5.6 meters/sec) were considerably decreased compared to the normal values. The F-wave could not be elicited in the lower extremities in 16 of 19 patients with Charcot-Marie-Tooth disease. The FWCV was normal in 10 patients with multiple sclerosis including 3 with clinical findings suggesting demyelination in the conus medullaris.