Myotonic dystrophy, also known as dystrophia myotonica (DM) or Steinert's disease, is a form of muscular dystrophy. Muscular dystrophies, or myotonias, are a group of conditions that cause progressive weakening of the muscles. The symptoms of myotonic dystrophy can vary widely due to the involvement of many systems in the body. One of the most distinguishing symptoms is muscle stiffness; muscle relaxation, which normally occurs after muscle contraction, is markedly delayed in this condition, resulting in general stiffness. This can be demonstrated by a patient trying to relax his or her hand after gripping an object for a sustained period of time. In myotonic dystrophy, the patient would be unable to immediately relax the grip without assistance.
Myotonic dystrophy symptoms begin in the face, progressing downward to the shoulder girdle. Later, movements of the foot, such as dorsiflexion, are lost. The facial manifestations of myotonic dystrophy symptoms include a characteristic "hatchet-faced" appearance. This physiognomy appears as a hollowing of the muscles around the temples due to the temporalis muscle involvement with a "hooding" of the eyes. In more advanced stages, the lower half of the face sags, with a drooping of the bottom lip as a result of masseter and orbicularis oris muscles atrophy.
Another distinguishing feature of Myotonic dystrophy is that the proximal muscles remain relatively stronger than their distal counterparts throughout the course of this disease. Although, weakness of the quadriceps can present in a number of patients. For instance, a patient may have relatively strong leg muscles but a profound weakness of ankle dorsiflexion, resulting in a striking foot drop.
Early myotonic dystrophy symptoms can include a weakness of the neck muscles, especially the sternocleidomastoids and flexors. Frontal pattern baldness is another early manifestation, along with a severe weakening of the muscles of the distal extremities. Later manifestations include tongue and pharyngeal involvement, resulting in a nasal voice, severe swallowing problems and dysarthric speech patterns, in which a patient would have difficulty articulating words.
Myotonic dystrophy symptoms also present in other systems of the body, especially in the circulatory system. Cardiac disturbances are quite common in myotonic dystrophy, especially patients with the DM1 type. These heart problems center largely in electrical disturbances of the myocardium, or cardiac muscle. First-degree heart blocks are common as well. Complete heart blocks are less common than first-degrees, but still can occur in a good number of patients. Other heart abnormalities, such as congestive heart failure and pulmonary heart disease, can also occur.
In fact, various systems within the body are affected during the course of myotonic dystrophy. For example, metabolic problems such as insulin resistance and diabetes are common. Gastrointestinal disorders including constipation and decrease of GI motility can occur as well. Myotonic dystrophy also produces mental impairments, leading to cognitive dysfunction and hypersomnia. Testicular atrophy and cataracts can also present in this condition.