Clinical Presentation Of Myasthenia Gravis


Patients with myasthenia gravis come to the physician complaining of specific muscle weakness and not of generalized fatigue. Ocular motor disturbances, ptosis or diplopia, are the initial symptom of myasthenia gravis in two-thirds of patients; almost all had both symptoms within 2 years. Oropharyngeal muscle weakness, difficulty chewing tough, chewy or fibrous foods, swallowing, or talking, is the initial symptom in one-sixth of patients, and limb weakness in only 10%. Initial weakness is rarely limited to single muscle groups such as neck or finger extensors or hip flexors. The severity of weakness fluctuates during the day, usually being least severe in the morning and worse as the day progresses, especially after prolonged use of affected muscles.
The course of disease is variable but usually progressive. Weakness is restricted to the ocular muscles in about 10% to 40% of cases. The rest have progressive weakness during the first 2 years that involves oropharyngeal and limb muscles. Maximum weakness occurs during the first year in two-thirds of patients. In the era before corticosteroids were used for treatment, approximately one-third of patients improved spontaneously, one-third became worse, and one-third died of the disease. Spontaneous improvement frequently occurred early in the course. Symptoms fluctuated over a relatively short period of time and then became progressively severe for several years (active stage). The active stage is followed by an inactive state in which fluctuations in strength still occurred but are attributable to fatigue, intercurrent illness, or other identifiable factors. After 15 to 20 years, weakness often becomes fixed and the most severely involved muscles are frequently atrophic (burnt-out stage). Factors that worsen myasthenic symptoms are emotional upset, systemic illness (especially viral respiratory infections), hypothyroidism or hyperthyroidism, pregnancy, the menstrual cycle, drugs affecting neuromuscular transmission, and increases in body temperature.

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