Quantitative correlation between plasma pyridostigmine levels and neuromuscular function in myasthenia gravis.

In 10 patients with myasthenia gravis, we studied the relationship between plasma pyridostigmine levels and five measures of neuromuscular function (NMF) following single oral doses of 60 to 120 mg. The NMF measures were percent decrement of the evoked muscle compound potential, maximum force, force-time integral, vital capacity, and outstretched-arm time. The combined mean improvement was most significant 2 hours after pyridostigmine ingestion and coincided with the peak plasma pyridostigmine levels in eight patients. In seven patients, there was a positive correlation between plasma pyridostigmine levels and the mean percent improvement.

Quantifying human muscle strength, endurance and fatigue.

Physiologic methods have been developed to objectively quantify muscle strength, endurance, and fatigability. Isometric force and rectified/integrated electromyogram were simultaneously recorded during the three phases of a recording session: pre-fatigue, fatigue (1 min duration) and post-fatigue recovery (up to 10 min). Five parameters of muscle performance were computed: Maximum force (MF) exerted during isometric voluntary contraction (muscle strength); Force-time integral--area under force-time plot (endurance); Fatigue index (FI) (% reduction in MF); Neuromuscular efficiency (force/mV of EMG recruited), and Recovery time (RT). Normal values based on data from 20 normal subjects were determined for four muscles: index finger abductor, elbow flexors, knee extensors, and ankle dorsiflexors. Neuromuscular efficiency (NME) decreased significantly (20 to 70%) at the end of the fatigue phase; it generally increased to the pre-fatigue level in 2 to 10 min, during the recovery phase. The period needed to reach pre-fatigue level was referred to as RT. The elbow flexors had the highest mean FI (48%) and the longest RT (greater than 6 min); the ankle dorsiflexors had the lowest mean FI (34%) and the shortest RT (1.5 min). These methods have been used also to evaluate the effects of weight training in two patients with neuromuscular disorders.

Emery-Dreifuss muscular dystrophy with autosomal dominant transmission.

A woman with early-onset, slowly progressive, humeroperoneal muscle weakness had marked restriction of neck flexion with contracture at the elbows. She developed exertional dyspnea at age 25, atrial fibrillation with slow ventricular rate was discovered, and a cardiac pacemaker was implanted. Her father had a similar disorder. There is at least one other report of autosomal dominant transmission of this clinical picture, which had previously only been reported as Emery-Dreifuss muscular dystrophy with X-linked recessive inheritance. Thus, more than one mode of inheritance is possible for this unusual and distinctive form of muscular dystrophy.