The term myopathy refers to a muscle fiberdisorder that can have a variety of etiologies. Myopathies present as pure motor syndromes without any disturbance of sensory or autonomic function. Deep tendon reflexes are usually preserved. In most myopathies, symptoms tend to be bilateral and affect proximal muscles preferentially, although there are exceptions. Because many myopathies cause progressive impairment of patients’ daily functioning, supportive therapy is often necessary to address the physical and psychological effects of these disorders. The final section of this chapter outlines strategies that are often used in rehabilitation of patients with myopathies.
EVALUATION OF MYOPATHIC DISORDERS
By far the most frequent symptom of patients presenting with myopathic disease is weakness. Clinically, it is important to differentiate weakness from easy fatigability. A hallmark of myopathy is the inability to generate a forceful contraction. It is important to observe patients performing activities such as walking, climbing stairs, and arising from a sitting, kneeling, squatting, or reclining position or using the arms overhead. Difficulty in performing these tasks signifies weakness rather than fatigue. Patients with complaints of fatigue often describe a subjective loss of energy. In myopathic disorders, objective muscle weakness and loss of function usually accompany fatigue. Pathologic fatigue not accompanied by muscle cramps upon exercise testing or repetitive electrophysiologic testing usually suggests a disorder of the neuromuscular junction (such as myasthenia gravis or Lambert-Eaton myasthenic syndrome), rather than a myopathy. If the patient develops fatigue along with frank swelling and cramps with exercise, then certain metabolic myopathies may be suspected.
Myalgias (muscle pain) and muscle aches may be a presenting complaint in patients being evaluated for myopathy. Most myopathies and muscle diseases are not associated with severe myalgias or muscles that are very tender to palpation. Severe myalgias and tenderness often accompany fasciitis, infectious myositis, and some metabolic myopathies.
Myopathies can be classified as hereditary or acquired. Information about the progression of the disease process is very important in helping to classify the specific etiology of myopathy. In patients who have deteriorating strength, it is important to make note of whether the rate of progression is over days, weeks, months, or years. A detailed family history and pedigree chart is very useful in clarifying suspected hereditary myopathies. Table 18–1 contrasts the key features of various hereditary and acquired myopathies.
Table 18–1Etiology of myopathies. ||Download (.pdf) Table 18–1 Etiology of myopathies.
|Hereditary Myopathies |
|Muscular Dystrophies ||Congenital ||Metabolic |
Glycogen storage diseases:
Type II—acid maltase deficiency (Pompe’s disease)
Type V—myophosphorylase deficiency (McArdle’s disease)
Type VII—phosphofructokinase deficiency
|Acquired Myopathies |
|Inflammatory ||Toxic ||Associated with Systemic Disease |
Inclusion body myositis