The motor unit and electromyography--the legacy of Derek Denny-Brown.

With the development of the concept of the motor unit and new recording instruments, single motor unit action potentials (MUAPs) were recorded in 1929 in man by Adrian and Bronk and in the experimental animal by Denny-Brown. Studies of MUAPs in patients with neuromuscular disease followed, and in 1938, Denny-Brown and Pennybacker laid the foundation for clinical electromyography (EMG). Action potentials of single contracting or spontaneously firing motor units, termed fasciculations, were recorded and separated from the action potentials of single denervated muscle fibers, termed fibrillations. Thus, it was possible to interpret muscle twitching and cramping by EMG and separate neurogenic from myopathic diseases. Since then, EMG and neuromuscular disease have expanded greatly providing greater diagnostic capability and therapeutic success.

Predictable recovery from myasthenia gravis crisis with plasma exchange: thirty-six cases and review of current management.

Adult, acquired, idiopathic, autoimmune myasthenia gravis has a well-characterized IgG anti-acetylcholine striated-muscle receptor antibody. Removal by plasma exchange is effective, established therapy to augment anti-cholinesterase and immunosuppressive therapy and is the treatment of choice for myasthenia gravis crisis. We report 36 consecutive patients referred and accepted for plasma exchange, 32 of whom were in or entering myasthenia crisis, over a 10 year period. An average of 7.8 (range 1 to 16) plasma exchange procedures were done, with uniform, significant improvement, including extubation of 13 in myasthenic crisis and discharge from hospital in all. We conclude that this is the best treatment for myasthenia gravis crisis in hospital. From recent cases, most, if not all, crises can be prevented by IVIgG or plasma exchange as out-patients with use of corticosteroid and or azathioprine.

Pulse cyclophosphamide therapy in chronic inflammatory demyelinating polyneuropathy.

Fifteen patients with chronic inflammatory demyelinating neuropathy (CIDP) were treated with pulse intravenous cyclophosphamide (IVCY) monthly for up to 6 months. Eleven patients reached a complete remission; only one patient worsened. Complications included nausea, vomiting, anemia, and hair loss. This case series suggests that monthly IVCY is beneficial in the treatment of CIDP and warrants a controlled study.

Painful trigeminal neuropathy: clinical and pharmacological observations.

UNLABELLED: A 74-year-old woman had a 5-year history of constant burning pain and numbness of the central face of subacute onset. The central region of the face, oral cavity, and nose lacked all sensation. Corneal reflexes and the jaw jerk were absent. Blood tests, rectal biopsy, neurodiagnostic studies, and surgical exploration of the trigeminal nerve were normal. Blink reflexes were absent. Facial nerve motor latencies and EMG of the facial and masseter muscles were normal. Responses to the thermoregulatory sweat test, intradermal histamine, and simulated diving were present. Oral administration of 500 mg L-dopa aggravated her pain and produced transient hypalgesia in the C2 through C6 dermatomes. Infraorbital nerve biopsy demonstrated loss of large myelinated fibers. IN CONCLUSION: (1) Only the central region of the face is exclusively supplied by the trigeminal nerves. (2) Somato-autonomic reflexes coupled with electrophysiological studies localized the lesion to the large fibers. (3) Large fiber loss and central brain stem reorganization may explain the burning pain. (4) Dopamine may modulate trigeminal nociception.

Temperature-sensitive repetitive discharges in paramyotonia congenita.

A 47-year-old female with paramyotonia congenita was studied with electromyography and showed minimal myotonic discharges but prominent repetitive discharges in hand muscles at room temperature. With cooling the hand, the repetitive discharges ceased as the myotonic potentials became prominent. With exercise and further cooling, the myotonic discharges increased and the strength of the muscle and recruitment pattern decreased. With warming, the myotonic discharges decreased as the repetitive discharges reappeared. This is the first report of repetitive discharges occurring in a patient with temperature-sensitive sodium channel myotonia. It is postulated that the repetitive discharges as well as the myotonic discharges are the manifestation of muscle membrane hyperexcitability secondary to the abnormal, noninactivating sodium channels.

Electrophysiological studies in Guillain-Barré syndrome: correlation with antibodies to GM1, GD1B and Campylobacter jejuni.

A retrospective study of 50 patients with Guillain-Barré syndrome (GBS) correlated analysis of serial motor nerve conduction studies with the presence of antibodies to Campylobacter jejuni, GM1 and GD1b, determined by ELISA. GBS patients with antibodies to C. jejuni (n = 8), GM1 (n = 4), or GD1b (n = 4) showed electrophysiological features suggestive of demyelination with prolonged distal motor latencies and temporal dispersion/conduction block similar to GBS patients without these specific antibodies. Three of 50 GBS patients had poor recovery with inability to walk at 1 year after onset of symptoms. All three patients had antibodies to C. jejuni, but not to GM1 or GD1b. Although later on in the clinical course distal motor responses were absent in two of these patients, reflecting extensive axonal degeneration, early nerve conduction studies showed findings suggestive of demyelination. We suggest that demyelination of peripheral nerve may be the initial disease mechanism in GBS independent of the presence of antibodies to C. jejuni, GM1 or GD1b.

Central motor reorganization after anastomosis of the musculocutaneous and intercostal nerves following cervical root avulsion.

In 4 patients with a complete upper limb palsy due to traumatic cervical root avulsion, surgical anastomosis of intercostal to musculocutaneous nerves was performed to restore function in the biceps brachii muscle. Four to 6 months after the operation, motor unit discharges were recorded from the biceps muscle on the operated side during deep breathing and by cortical magnetic stimulation. The motor unit discharges became independent from respirations gradually over 1 to 2 years. The latencies of the motor potentials evoked by cortical and thoracic root magnetic stimulation decreased gradually over 2 to 3 years. Motor cortex mapping of the reinnervated biceps muscle showed a gradual change over 4 to 33 months from the area of the intercostal muscles to that of the arm area, which was more lateral on the motor cortex. These findings suggest that reorganization of the motor cortex to arm flexor muscles occurs following peripheral nerve anastomosis.

Sweat function in Parkinson's disease.

Sweat function was studied in patients with Parkinson's disease and in normal adults by sympathetic skin response, the bromphenol blue printing method and the silicone mould method. In patients with Parkinson's disease, dysfunction of sweating was classified into two types: one type involved the postganglionic fibres and the other involved the preganglionic fibres or the central nervous system. The latter was observed in patients with milder disease and the former was observed in patients with severe disease. The progressive involvement of sweat function in Parkinson's disease may reflect spread from the central nervous system or preganglionic fibres to postganglionic fibres. In a few patients the results of sweat tests were normal. Ceruletide increased sweating in Parkinson's disease patients, and decreased the prolonged latency of the sympathetic skin response. It is hypothesized that ceruletide facilitates the preserved somatosympathetic reflex of sweating.