Simply Stated: Stiffness, Cramps and Twitching
Neuromuscular diseases can cause a variety of symptoms other than muscle weakness. Some people may feel their muscles are stiff or don't respond quickly; others might complain of cramps or twitches; while still others get tired quickly during exercise.
Not all of these symptoms are painful, but some can be inconvenient or annoying. Learning the medical names and natures of these symptoms can lead to better discourse between you and your doctor, and sometimes better management of symptoms.
A true cramp is a specific condition in which muscles undergo painful involuntary contractions (muscle shortening). The classic muscle cramp is neural in origin, meaning the contractions are caused by abnormal nerve activity rather than abnormal muscle activity. This type of contraction problem usually has a sudden onset and may be ended by stretching the muscle passively.
True cramps can occur in anyone, particularly after exercise or at night. Neuromuscular diseases in which classic cramps are common are amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA).
A second kind of cramp, which doesn't involve abnormal nerve activity, occurs when a muscle is temporarily locked in a contracted state. This is technically called a contracture, but isn't to be confused with the more common use of "contracture" to indicate fixed joints.
This sensation can be painful and is often described as a cramp. People with paramyotonia congenita, some forms of myotonia, rippling muscle syndrome or metabolic myopathies due to glycolytic defects (McArdle's disease, Cori's or Forbes' disease, Tarui's disease, phosphoglycerate kinase deficiency and lactate dehydrogenase deficiency) may experience muscle pain during exercise due to nonneural muscle cramps.
"Fasciculation" is basically a fancy term for a twitch. Like classic cramps, fasciculations are caused by abnormal nerve activity, but they tend to involve only a small portion of the affected muscle and aren't generally painful.
While one is occurring, you may observe a small muscle "jump" under the skin. Fasciculations are common in ALS, spinal bulbar muscular atrophy, X-linked SMA and SMA type 1 (in the tongue and mouth).
Neurologist Valerie Cwik of the University of Arizona Health Sciences Center in Tucson says that everyone gets fasciculations now and then, particularly around the eye, in the small muscle of the back of the hand between the thumb and index finger, and in the feet.
Fasciculations are made worse by stress, lack of sleep and caffeine. They may also be seen in people with overactive thyroids, and there's a syndrome of benign (harmless) cramps and fasciculations. While some people with cramps and fasciculations develop ALS, in others the problem remains restricted to these symptoms.
Myotonia occurs when contracted muscles relax too slowly due to electrical problems in the muscle or nerve cells. A person with myotonia may have difficulty releasing his grip after holding an object — the sensation is sometimes described as stiffness. Myotonia can be sensitive to exercise, temperature or diet, and occurs in paramyotonia congenita (PC), myotonia congenita (MC), hyperkalemic periodic paralysis (PP) and myotonic dystrophy (MMD).
Myalgia, or muscle pain, can be caused by mechanical stress without muscle injury (as in classic or nonneural muscle cramps), or by injury. Muscle injury can occur in anyone who "overdoes it" during exercise, including those with types of muscular dystrophy that render muscle cells more fragile.
Muscle injury can also occur in response to problems with the immune system, as in polymyositis and dermatomyositis, or in response to a lack of energy and buildup of toxic metabolites, as in carnitine palmityl transferase deficiency.
Fatigue can mean a subjective feeling of tiredness or an objective measurement of a decline in muscle force with use, but is always distinguished from weakness. Fatigue is associated with myasthenia gravis, ALS, SMA, myotonic disorders, metabolic disorders (McArdle's and Tarui's diseases) and mitochondrial disease. It can be a feature of many of the muscular dystrophies as muscles weaken and greater energy is expended to move them.
Hypotonia means "lack of muscle tone," or absence of the normal degree of tension in the muscle at rest. The condition is seen most often in infants and children with neuromuscular problems, who may appear "floppy" because of the lack of muscle tone.
Hypotonia can occur in many muscle disorders, including acid maltase deficiency, mitochondrial disorders, congenital myopathies (central core disease, nemaline myopathy and myotubular myopathy), congenital myotonic dystrophy, congenital muscular dystrophies, neonatal and infantile myasthenia gravis, SMA type 1 and "benign" congenital hypotonia.
These muscle symptoms have many different primary causes. Although not all can be treated, some respond to gentle stretching, heat or cold, while others may respond to drug treatments. Your MDA clinic director will help you identify and possibly treat these symptoms.
"Simply Stated" is a Quest column designed to explain some terms and basic facts about neuromuscular disease.
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