A 48-year-old woman was referred for evaluation of myalgias. She had muscle problems dating to childhood. She tired easily and was unable to keep up with her peers in athletic events. Shortly after beginning to exercise, she experienced weakness and a burning sensation in her muscles. She could not complete assigned running tasks in the allotted time and frequently became nauseated and sometimes vomited after running. She was labeled as a "slacker" because of this behavior. No cola-colored urine was noted during these events. Symptoms improved with rest; however, she also developed myalgias at rest as an adult.
Over the past few years, she developed fixed proximal weakness manifest as difficulty combing her hair and climbing stairs, and she had difficulty peddling a bicycle. The myalgias and fatigue interfered with her ability to work in a packaging plant. She also had difficulty sleeping that improved with amitriptyline administration.
Previous neurologic evaluations disclosed elevated creatine kinase (CK) levels (two to three times normal) on several occasions. An electromyogram (EMG) of limb muscles was normal. A deltoid muscle biopsy specimen, which was evaluated at a referral center, was interpreted as showing type II muscle fiber atrophy and non-specific changes suggestive of myopathy including subsarcolemmal red staining with Gomori trichrome. Electron microscopy revealed focal collections of both enlarged mitochondria and glycogen. Serologic testing for connective tissue diseases was negative. The thyroid stimulating hormone was minimally elevated.
There was a history of endometriosis and tobacco use. Her father had rheumatoid arthritis. A brother and his daughter have myalgias, but they have not been evaluated. Another brother has lymphoma.
On our examination, mental status, cranial nerves, sensation, and tendon reflexes were normal. There was Medical Research Council (MRC) 4+ strength in the deltoids, biceps brachii, wrist extensors and flexors, and iliopsoas. She had difficulty arising from a squat. There was no organomegaly.
Serum carnitine and lactate levels were normal. An ischemic lactate test was not performed.
Our needle EMG examination revealed 1+ to 2+ positive waves, fibrillation potentials, and occasional complex repetitive discharges in paraspinal muscles at four levels. In contrast, there was only irritability without spontaneous activity limited to two of seven limb muscles. There were scattered short duration motor unit potentials in some proximal muscles.
DIAGNOSIS & DISCUSSION