Background: Acquired myasthenia gravis (MG) is the most common neuromuscular junction disorder. Acetylcholine receptor (AChR) antibody is found in the majority of MG.

Objective: Describe and compare the clinical manifestations of MG patients with and without the presence of serum AChR antibody.

Material and Method: Between 2009 and 2010, 90 cases with MG, treated at the adult neurology service of King Chulalongkorn Memorial Hospital were consecutively recruited. Serum AChR antibody was measured by enzyme linked immunosorbent assay. Result of 0.45 nmole per liter or over is considered positive. Patients were divided into two groups based on serological status. Demographic data and clinical parameters were recorded and compared.

Results: Mean age was 47.5 + 15.6 years. Sixty-eight (75.5%) were female. Twenty-two (24.4%) had ocular MG and sixty-eight (75.6%) had generalized MG. Mean age of onset was 40.9 + 15.2 years. Sixty-seven (74.4%) were AChR antibody positive and twenty-three (25.6%) were AChR antibody negative. Limb/ocular-limb weakness was more commonly found in AChR antibody positive (p = 0.12) while pure ocular weakness was significantly found in AChR antibody negative (p = 0.006*). Myasthenic crisis (MC) tended to develop in AChR antibody positive (p = 0.06). Numbers of patients with moderate to severe weakness were significantly higher in AChR antibody positive (p = 0.04*). Thymic pathology was found in 72.3% of thymectomized AChR antibody positive patients. None of thymectomized seronegative patients had abnormal thymus. Good response to acetylcholine esterase inhibitors was more frequent in AChR antibody positive patients (p = 0.009*). Immunotherapy and thymectomy (p = 0.001*) were more frequently provided in AChR antibody positive patients.

Conclusion: AChR antibody positive MG manifested more severe, generalized weakness with frequent MC. Abnormal thymic histopathology was more frequently found in AChR antibody positive MG. Response to ACEI was better in AChR antibody positive group. However, overall outcomes of both groups were favorable without any difference.

Keywords: Myasthenia gravis, Acetylcholine receptor antibody, Clinical manifestation