21. Myasthenia gravis and multiple sclerosis: An uncommon presentation

Abstract

Myasthenia gravis (MG) is an autoimmune disease that compromises neuromuscular transmission and is mediated by autoantibodies against acetylcholine receptors on the postsynaptic membrane 1. In its usual form it leads to symptoms of decreased muscle strength and fatigue 1. Multiple sclerosis (MS) is an immune-mediated demyelinating disease of the central nervous system that shows a wide range of clinical features and a variable natural history 2. There is some evidence that patients with MG or MS have a higher risk of developing autoantibodies and other neu-roimmune disorders than normal controls 3,4. An autoimmune pathogenesis is implicated in both MG and MS, but the coexistence of the two disorders has rarely been documented, and for this reason we report this case 4. CASE A 28-year-old woman presented with diplopia, dysphagia and mild limitation of ocular movements, with progressive palpebral ptosis and weakness, which changed in intensity from day to day and during the day according to the patient's physical activity. Physical examination did not reveal any abnormalities. On neurological examination she was found to have asymmetrical palpebral ptosis (left>right); symmetrical muscle weakness (grade 4 on the MRC scale) in the proximal upper and lower limbs; and deep tendon reflexes. Gait and all sensory examinations were normal. The investigation yielded the following results: (1) positive anti-acetylcholine receptor antibody test (14.91 nmol/L; normal < 0.20 nmol/L); (2) normal needle electromyography and nerve conduction studies; (3) repetitive stimulation of the facial, spinal accessory and ulnar nerves at 3 Hz with a decrement of more than 10% in compound muscle action potential amplitude (Fig 1); and (4) improvement of symptoms after treatment with pyridostigmine (180 mg daily). Chest computed tomography scan was normal. A diagnosis of MG was made, and the patient showed an improvement in symptoms after she started to receive prednisone and pyridostigmine. Prednisone was discontinued after one year and was followed by oral administration of azathioprine (100 mg/day), with an improvement in palpebral ptosis and muscle strength (grade 5 on the MRC scale). When she was 32 years old and still on azathioprine treatment , the patient developed a sudden weakness in her left lower limb and was treated with prednisone (60 mg/day). After this new neurological manifestation suggestive of MS, the patient was submitted to brain magnetic resonance imaging (MRI), which revealed multiple areas of high signal on FLAIR and T2-weighted images in the periventricular and subcortical white matter of the brain hemispheres (Fig 2A). Fig 1. Repetitive stimulation at 3 Hz showing a 26.3% amplitude dec-rement in compound muscle action potential in the facial nerve recorded from the orbicularis oculi muscle (A), a 24.4% decrement in the spinal accessory nerve recorded from the trapezius muscle (B), and a 12.3% decrement in the ulnar nerve recorded from the abduc-tor digiti quinti muscle (C).