While the main manifestations of this group of disorders, muscular cramps, would seem to belong in this chapter on muscle diseases, they are, in fact, related to disorders of motor nerves, axons, and their terminal arborizations. For this reason, they appear in Chap. 46 on channelopathies and in Chap. 43, with disorders of the peripheral nerves.
Many of the muscle diseases described previously are associated with aching and discomfort. These are particularly prominent in conditions that are accompanied by cramp and biochemical contracture (phosphorylase and phosphofructokinase deficiency). Ischemia of muscle—that is, intermittent claudication—is also painful, as is dystonia in some cases. Muscle weakness that imposes persistent abnormal postures on the limbs may cause stretch injury to muscles and tendons. This is observed in a number of the congenital myopathies and dystrophies. In all these conditions, clinical study will usually disclose the source or sources of the pain.
Diffuse muscle pain, which merges with malaise, is a frequent expression of a large variety of systemic infections—for example, influenza, brucellosis, dengue, Colorado tick fever, measles, malaria, relapsing fever, rheumatic fever (in which it was called “growing pains”), salmonellosis, toxoplasmosis, trichinosis, tularemia, and Weil disease. When the pain is intense, especially if it is localized to one side of the lower chest and abdomen, the most likely diagnostic possibility is epidemic myalgia (also designated as pleurodynia, “devil’s grip,” and Bornholm disease caused by Coxsackievirus infection). Poliomyelitis may be accompanied by intense pain at the onset of neurologic involvement, and later the paralyzed muscles may ache. This is true also of the Guillain-Barré syndrome, in which the pain may precede weakness by several days. Little is known about the pathologic basis of the muscular pain in these diseases; it is not a result of muscle inflammation and is probably produced by circulating cytokines that are common to most systemic infections. Mild muscle pain is a frequent but not a necessary accompaniment of polymyositis and dermatomyositis.
Polymyalgia Rheumatica (See Chap. 10)
The major consideration in elderly and middle-aged patients with pain in proximal muscles of the limbs is polymyalgia rheumatica. This subject is mentioned briefly in other sections of this book in relation to back and extremity pain (see Chap. 10) and to temporal arteritis, to which it is closely connected (see Chap. 9). The muscular soreness may be diffuse or asymmetrical, particularly in the proximal arms and shoulders. Every movement is reported as stiff and painful. The periarticular tissues and their muscular attachments are affected primarily and may be tender, but this is difficult to interpret, because tenderness in these regions may be found in healthy individuals. The sedimentation rate is elevated in the majority of patients, and a 48-h trial of prednisone, by completely alleviating muscle pain, confirms the diagnosis. In the context of muscle pain, systemic symptoms such as weight loss, headache, and fatigue, as well as mild anemia, are particularly suggestive of polymyalgia rheumatica.