This is usually associated with crampy pain of the muscles and other findings of hypothyroidism. Of interest, lithium does interfere with uptake by the thyroid of iodine. Specifically there is interference with the iodination of tyrosine and the synthesis of thyroxine. The patient's thyroxine level may be slightly decreased and the thyroid stimulating hormone increased. Most patients, however, remain euthyroid but may develop a goiter.
Alcohol is also a cause of myopathy.
Differentiating between myopathies and neuropathies is possible on a clinical basis, but may be difficult. Toxic peripheral neuropathies are usually diffuse, and symmetric. Most toxic neuropathies are axonopathies. Sensory and motor fibers are involved and distal dysesthesias predominate on presentation. Pure motor axonopathies do exist but are rare.