A Woman With Proximal Muscle Weakness, Calf Hypertrophy, Heel Contractures, and Elevated Serum Creatine Kinase

A 23-year-old obese White woman was referred because of weakness in the legs, an EMG that showed a “myopathy,” and a very elevated serum creatine kinase (CK) level. She had normal thyroid-stimulating hormone and FANA and a normal spinal MRI.

She stated that she had walked on her toes since age 10 and was seen by an orthopedic surgeon who placed her in braces for years. She later noticed difficulty going upstairs, bending, and squatting and had a tendency to fall; she had no numbness. There was no family history of neurologic disorders.

Neurologic examination revealed normal mentation and cranial nerves. She had mild hypertrophy of the calf muscles, contractures of the ankles, and difficulty walking on her heels and rising from a chair ( Fig. 81-1 ). Manual muscle testing revealed 4/5 neck flexor weakness and 5−/5 in shoulder extension and abduction; biceps and triceps were 5/5; hip flexors, abduction, and extensors were 4/5; thigh muscles were 5−/5; and foot dorsiflexion was 4−/5; foot flexion, inversion, and eversion, and other muscle groups were normal. Reflexes and sensory examination were normal.

What is the Differential Diagnosis?

This patient had a long-standing history of muscle weakness since childhood with contractures of the heel cords and large calves. The differential diagnosis includes spinal muscular atrophy, although the previous report of a “myopathic” EMG and the elevated CK suggests that she had a primary myopathy. Her long-standing history made inflammatory myopathy unlikely. There was no history of hypotonia or early-childhood-onset weakness to suggest a congenital myopathy, although nemaline or rod myopathy, myotubular myopathy, and central core disease could have their initial manifestation in late childhood or even adulthood. The rather high CK, however, makes most of these myopathies unlikely. Metabolic myopathies, such as acid maltase deficiency and mitochondrial disorder, cannot be ruled out. However, they usually do not have calf hypertrophy, and there was no evidence of extraocular muscle impairment, decreased hearing, or other systemic manifestations to suggest the latter. Endocrine myopathies, particularly hypothyroidism, manifest with an elevated CK, but the patient’s thyroid-stimulating hormone was normal.

Other possibilities include limb-girdle muscular dystrophy or the manifest carrier state of a dystrophinopathy, in spite of the negative family history.