There are also conditions that cause progressive loss of motor nerve cell bodies, known as the anterior horn cells, which can cause progressive weakness and muscle wasting known as motor neuron disease, Amyotrophic Lateral Sclerosis or “Lou Gehrig’s” disease. Electrodiagnostic (EMG/NCS) study can easily determine if this is the case, but can often differentiate this serious diagnosis from many other treatable muscle and nerve conditions that can mimic it
While diseases of muscle are much less common, there are many muscle disorders to include a host of ‘sick muscle’ problems known as myopathies, myotonias, and muscular dystrophies. All these can cause progressive weakness, at times muscle cramping, and functional losses. While EMG cannot always differentiate one myopathy from another, it can often identify if a myopathy is present or not, and if so, how active and severe, while also identifying if a nerve problem is causing weakness as opposed to a muscle problem. At times our bodies make auto-antibodies targeted against muscle tissue that results in active muscle inflammation and in turn damage, known as polymyositis. This is a problem which can often be effectively treated once identified.
Finally, there are rare disorders that affect the linkage between the motor nerve terminal and the muscle it is supplying that allows for muscle contraction. This synapse is known as the neuromuscular junction. There are a few disorders that impair the ability of this nerve – muscle junction to function properly which can cause both localized, as well as diffuse weakness to include of swallowing and breathing. One disorder is an auto-immune process where by auto-antibodies are directed against the muscle membrane preventing nerve impulse transmission, known as Myasthenia Gravis. Due to medical progress, this is a problem that nowadays usually has effective treatment. A much more rare disorder also produces antibodies, although these directed at the nerve terminals resulting in a problem known as Lambert–Eaton Myasthenic Syndrome