Juvenile Myasthenia Gravis- A rare case report

Abstract

Background : It is an acquired autoimmune mediated postsynaptic disorder that is rare in childhood with prevalence of 5 in 1,00,000. First case was reported in the year 1644 in USA of an Indian chief Opechankanough. The disease is due to circulating antibodies which bind to acetylcholine receptors at neuromuscular junction and prevent a normal action of acetylcholine in opening the calcium channel in muscle fibers. There are two types of the disease: ocular (corresponding to 10% of cases) [1] or generalized (90% of cases), although both may occur under different temporal evolution in the same patient. Myasthenia gravis geoepidemiology shows that it is a rare disorder with similar incidence and prevalence in the world, except for infantile MG, which is more common in Asia. Methods : With progressive ptosis towards the end of the day, Juvenile Myasthenia gravis was suspected. Anti cholinesterase (AChE) test was done under ECG monitoring using intravenous injection of neostigmine (Prostigmine test) which showed a dramatic response i.e. immediate elevation of both upper eyelids with resolution of ptosis[Fig. 1 and 2]. Bed side icepack test was also performed which was positive. Computerized tomography (CT scan) of thorax was done to rule out thymic hyperplasia or thymoma. We diagnosed this child as a case of juvenile myasthenia gravis and treated with intravenous neostigmine(0.04mg/ kg/dose) 4 hourly followed by atropine(0.05mg/kg/dose) to counteract ill muscarinic side effects of neostigmine. Intravenous methylprednisolone was also given as pulse therapy (30mg/ kg/day for 3 consecutive days) with multipara monitoring (for hypertension and hyperglycemia). Plasma anti-AChR antibodies though advised was not affordable. Results : The cardinal symptom in MG is muscle weakness that is typically fluctuating and fatigable. The most common initial presentation involves a specific muscle weakness, and not a generalized weakness. Symptoms are exacerbated with exercise (it may be caused by sustained muscle action) and heat, and decreased with relaxation and cooling. The disease involves striated or voluntary muscles, with a typical anatomical distribution. The weakness is usually ocular, bulbar, proximal muscle groups (most commonly the upper limbs) and neck, but may also in some patients involve the respiratory muscles. The disease can progress from mild to moderate to severe in weeks and months with episodes of exacerbations and remissions. The Myasthenia Gravis Foundation of America# proposed a clinical classification of the disease into five main classes and several subclasses, according to the location of muscle weakness and its intensity. Ptosis or extra ocular muscle weakness is the initial presentation in 75% of patients [1] and occurs during the course of the disease in 90% of cases (remaining exclusively ocular only 16% of cases [2-4]). When anti AChR antibodies are negative, MuSK receptor antibodies should be advised. Table 1 : Classification of MG according to Ossermann Scale Type 1 Ocular myasthenia characterized by ptosis and diplopia Type 2a Slow onset, frequently ocular, with gradual evolution to skeletal musculature Type 2b Slow onset with dysarthria, dysphagia, and change in mastication Type 3 Fast onset with severe bulbar and skeletal muscle fatigue with respiratory muscle compromise Type 4 Severe MG that manfests in two years Conclusion : Repetitive ulnar nerve stimulation (RNS) studies show significant decremental response in abductor digiti minimi suggestive of post synaptic neuromuscular junction (NMJ) receptor disorder[5]. Other differentials which should be considered include neuroparalytic snake bite, Miller-Fischer type of GBS and botulism. Our patient was classified as type III i.e. fast onset with severe bulbar and skeletal muscle fatigue with respiratory muscle compromise, so he had to be ventilated for 3 days. He was weaned from IPPV to T-piece over 12 hours and then to CPAP for 6 hours maintaining normal saturations and vitals. Thereafter he was referred to higher center for plasmapharesis but since then he is lost to follow up.