Neuromuscular Junction Disorders and Myopathies

Abstract

Complaints of weakness without sensory changes in the elderly must evoke the rare, but important, diagnostic categories of motor neuron disease (MND), neuromuscular junction (NMJ) disorders and myopathies. In this chapter we will discuss the last two diagnostic categories, with MND being covered elsewhere. These patients may present with ptosis, diplopia, dysphagia, dysarthria, dyspnea, muscle atrophy and weakness. These complaints are usually not accompanied by other neurologic signs such as spasticity, rigidity, brisk reflexes, ataxia, sensory loss or significant pain. Although other processes such as congenital myasthenic syndromes, botulism poisoning, secondary myopathies from endocrinopathies or steroid use, and even muscular dystrophies can present after the age of 65, the more common neuromuscular junction disorders seen in the elderly include myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS); and the more common myopathies include inflammatory myopathies such as inclusion body myositis (IBM) and necrotizing myopathies. Clues such as fluctuating weakness, slowly progressive weakness, distinct patterns of weakness, and laboratory and electrodiagnostic studies often help in the diagnosis of these disorders. In this chapter, we will review the clinical presentation, diagnostic workup and treatment of MG, LEMS, IBM, the immune-mediated necrotizing myopathies, and briefly touch on dermatomyositis and polymyositis.