Via practica 6/2008

MYASTHENIA GRAVIS IN GENERAL PRACTITIONER´S OUT-PATIENTS´S DEPARTMENT

Myasthenia gravis (MG) is an uncommon autoimmune disorder caused by autoantibodies to the muscle acetylcholine receptors (AChR) or to muscle specific kinase (MuSK) at the neuromuscular junction. Autoantibodies are responsible for a defect in neuromuscular transmission, causing the characteristic fluctuating weakness and exhaustibility in voluntary muscles. Ocular, facial, oropharyngeal, shoulder, hip, trunk and limbs muscles may be involved in varying combinations and degrees of severity. Ptosis or diplopia is the usual initial symptom in 50 – 60% of patients. Difficulty in chewing, swallowing, or talking is the initial symptom in 20 – 30% of patients. In about 10 – 15% patients, the initial symptoms are due to weakness of single muscle groups, such as neck or finger extensors, hip flexors, or ankle dorsiflexors. Characteristic clinical features of MG are dramatic changes in severity of weakness over brief periods, typically worsening as the day goes on. Weakness also typically worsens after prolonged use of affected muscles. The course of MG is variable, but commonly progresses over time. Physical examination of patients with suspected MG must be performed in a way that will detect varying weakness in specific muscle groups. Diagnostic procedures that confirme the diagnosis of MG are intravenous administration of neostigmin, EMG and presence of autoantibodies to AChR and MuSK. Treatment of MG focuses on anticholinesterases, immunosuppressive agents, thymectomy an short-term interventions such as plasmapheresis and intravenous immunoglobulin. These treatments, usually in combination, produce remission or improvement in about 90% of MG patients.

Keywords: myasthenia gravis, muscle weakness and exhaustibility, symptoms, clinical examination, diagnosis, treatment.