A case series of false positive anti-acetylcholine receptor antibody

Abstract

Myasthenia gravis is an autoimmune neuromuscular disorder typically characterized by fluctuating weakness. Antibody-mediated immunologic attack in the postsynaptic membrane of neuromuscular junction is the key pathophysiology of the disease. Hence, anti-acetylcholine receptor (AChR) antibody test is very specific for myasthenia gravis. However, there are rare occurrences of false positive anti- acetylcholine receptor antibody. Here, we illustrated a case series of three different neurological diseases without typical courses of myasthenia gravis but having positive AChR antibody tests. Patient 1 was a 43-year-old woman presented with progressive lower limb weakness for eight months and bulbar symptom for one month and intubated for respiratory distress. She underwent intensive investigation, received steroid, plasmapheresis but not responded to treatment and required tracheostomy. She was finally diagnosed as motor neuron disease and was discharged with home ventilator. Patient 2 was a 67-year-old woman complained of progressive bilateral eye ptosis and ophthalmoplegia for 6 years without limb weakness and bulbar symptom. She did not respond to pyridostigmine. The repetitive nerve conduction study and single fiber electromyography were normal and was diagnosed as chronic progressive external ophthalmoplegia (CPEO). Patient 3 was a 50-year-old woman with recent tonsillitis presented with bulbar symptom, limbs weakness, ataxia, urinary and bowel retention. She received intravenous immunoglobulin (IVIG) and followed by plasmapheresis and steroid, responding well to treatment. Serial nerve conduction study was performed and she was eventually diagnosed as acute motor sensory axonal neuropathy, a variant of Guillain-Barré syndrome (GBS) with treatment related fluctuation. In conclusion, these cases illustrate the importance of clinical correlation with neurophysiological test. Presence of AChR antibody is not always equivalent to myasthenia gravis.