Congenital myasthenic syndromes: Natural history and long-term prognosis

Congenital myasthenia syndrome (CMS) is a rare, heterogeneous group of genetically determined, disorder of neuromuscular transmission. They have a varied presentation and progression and very few studies have addressed the natural history. Aim of the present study is to describe the clinical profile and natural history of patients with CMS.

Study includes patients with CMS who attended comprehensive-neuromuscular-clinic (CNMC) during the period January, 2000-2008 with a minimum follow-up of 2 years, with inclusion criteria: (1) Onset in infancy or childhood with fluctuating ocular, bulbar, respiratory or limb muscle weakness (2) Acetylcholine receptor antibody negative (3) normal computed tomography (CT) thymus (4) Abnormal repetitive nerve stimulation (RNS) testing (5) Exclusion of other autoimmune disorders.

Out of 314 patients with myasthenia who attended the CNMC during study period, 15 (4.8%) were with CMS (8 boys, 7 girls). Patients were divided as infantile and childhood onset. The mean age of onset and diagnosis in infantile and childhood onset groups were 5.5 months/3.1 years and 3.6 years/6.5 years respectively. Eleven patients had ptosis and 4 had generalized presentation. Most common site of decremental response was over facial nerve in 12 (75%) patients. All patients showed good response to treatment with acetyl cholinesterase inhibitor with stable course on follow-up without exacerbations. Mean dose for neostigmine was 28 mg/day and for pyridostigmine was 153 mg/day.

Ptosis is most common symptom at onset in CMS, emphasing importance of RNS of the facial nerve, in the absence of molecular diagnosis of CMS. Our CMS cohort had relatively stable course without intermittent exacerbations with fair response to acetyl cholinesterase inhibitor.