An Older Woman With Progressive Muscle Weakness

A 62-year-old woman presented with progressive muscle weakness for more than 6 years. She had been previously diagnosed with polymyositis; she was treated with corticosteroids without benefit and subsequently referred to us. The patient complained of difficulty going up and down stairs and in turning door knobs but denied any problems swallowing, muscle pains, or sensory complaints.

Past medical history was unremarkable; she did not smoke or drink alcohol.

General examination, mentation, and cranial nerves were normal; in particular, there was no evidence of facial weakness, tongue atrophy, or fasciculations.

There was moderate symmetrical atrophy of the biceps, triceps, and quadriceps muscles ( Fig. 100A-1 ). Manual muscle testing demonstrated MRC scoring in neck flexors of 5−/5, extensors, 5/5; shoulder muscles, 4+/5; biceps, 3+/5; triceps, 3/5; wrist extensors, 4/5; wrist flexors, 3+/5; finger extensors, 3−/5; flexors, 3−/5; and intrinsic hand muscles, 3+/5. In the lower extremities the iliopsoas muscles were 4/5; quadriceps, 3−/5; adductors, glutei, and hamstrings, 4/5; foot dorsiflexors and evertors, 4/5; and flexors, 5/5. Reflexes were 1+ all over, except for trace at the knees. Vibration, pinprick, and touch sensations were normal. No fasciculations were detected. There was no percussion or grip myotonia. The examination was otherwise unremarkable.

Blood tests revealed normal complete blood count; the serum creatine kinase (CK) was 360 IU/L (normal, <200 IU/L); comprehensive metabolic panel, thyroid function tests, FANA, and erythrocyte sedimentation rate were all normal.

What is the Differential Diagnosis?

This older woman presented with progressive weakness and mildly elevated serum CK. The differential diagnosis includes a motor neuron disorder, such as progressive spinal muscular atrophy, which could have a similar presentation, and mildly elevated CK, but the slow progression and lack of fasciculations are somewhat against that diagnosis. The long history of nonfluctuating weakness and atrophy, lack of cranial nerve abnormalities, and mildly elevated CK are also against a disorder of neuromuscular transmission, and she had no sensory deficits to suggest a polyneuropathy.

This patient appeared to have a progressive myopathy. The differential diagnosis of this is extensive and includes limb-girdle dystrophy, an endocrine or metabolic myopathy, and proximal myotonic myopathy (PROMM), even if there is no clinical myotonia. Inflammatory myopathies, such as polymyositis and inclusion body myositis (IBM), are also important considerations; the distribution of weakness, age, and the lack of response to steroids suggest the latter.