Last modified: 2018-09-09
Abstract
Introduction: Anti-acetylcholine receptor (AChR) antibody is pathogenic, highly sensitive and specific for autoimmune myasthenia gravis (AMG). Only a few false positive cases were reported to date. We had a case of a young child with positive anti-AChR antibodies on 2 separate sera, and was managed as refractory AMG but revealed later to have COLQ-mutant congenital myasthenic syndrome (CMS).
Case Description: A 4-month-old boy with hypotonia and bilateral ptosis was investigated for neuromuscular disorder. His anti-AChR antibody determined via ELISA (Euroimmun AG, Germany) at 6 months old was positive but maternal antibody titre was negative. Repetitive nerve stimulation and stimulated jitter analysis with concentric needle confirmed a neuromuscular junction disorder. A provisional diagnosis of AMG was made. However, he responded poorly to pyridostigmine and immunotherapy as he continued to have episodes of acute respiratory failure requiring invasive ventilator support. Anti-AChR antibody at 13 months old remained positive. The possibility of CMS was explored in view of unfavourable clinical progression, early onset phenotype and poor response to treatment. Pyridostigmine was withheld, and salbutamol introduced. He showed remarkable improvement at 14 months old. Additionally, CMS genetic testing confirmed presence of compound heterozygous COLQ mutation.
Conclusion: False-positive anti-AChR antibody in CMS has never been reported in medical literature. The above case provides support that CMS should be considered in children with early presentation and subsequent poor treatment response.