Muscle Radiography: Too Little, Too Soon
Abstract & Commentary
Source: Ozsarlak O, et al. Hereditary neuromuscular diseases. Eur J Radiol. 2001;40:184-197.
Muscle reactions to pathologic conditions are myriad and include, among others, cell death, regeneration, hypercontraction, split fibers, storage, and calcification. Clinical appreciation of these changes usually requires muscle biopsy and light or electron microscopy. Some changes, including atrophy, hypertrophy, pseudohypertrophy, and fatty infiltration, can be appreciated by computerized tomography (CT) and magnetic resonance imaging (MRI). How much information do these modalities provide and what do they add to the management of neuromuscular disease patients?
Muscle CT and MRI findings were reviewed from a large group of neuromuscular disease (NMD) patients including muscular dystrophy (Duchenne, Becker, limb girdle, facioscapulohumeral, Emery Dreifuss, congenital, merosin deficient, and myotonic), congenital myopathy, metabolic, inflammatory (inclusion body, polymyositis, and dermatomyositis), spinal muscular atrophy, and hereditary motor and sensory neuropathy. Fatty infiltration was the most common finding, falling into a variety of patterns. Central or peripheral zones of hypodensity, and generalized or diffuse patchy areas of low density (with or without preservation of peripheral fascia) were seen. None of the patterns were specific or diagnostic and all conformed to the clinical distribution of muscle abnormalities. Although not useful diagnostically, muscle radiography may assist in choosing which muscle to biopsy and in following disease progression.
Commentary
Ultrasonographic examination is a relatively simpler, more time efficient, and less costly method for evaluating muscle (Neuromusc Disord. 1999;9:203-207). Among 100 children with suspected NMD, 66 boys and 34 girls with a mean age of 5.3 years, ultrasound had a sensitivity of 78% and specificity of 91% in detecting NMD. In the younger than 3-year-old age group, sensitivity and specificity were even greater, 81% and 96%, respectively. Muscle ultrasound is specific and sensitive for uncovering suspected NMD in children. It also appears comparable to MRI, at least with respect to examining cross-sectional area or volume (Br J Sports Med. 1997;31;59-64). In a study of these measurements using MRI and ultrasound in the quadriceps femoris muscle of 10 healthy volunteers, no significant differences were discerned. Presently these methods have limited usefulness in the clinical neurology setting but further advances in their methodology may prove clinically valuable. —Michael Rubin, MD. Dr. Rubin, Associate Professor of Clinical Neurology, New York Presbyterian Hospital-Cornell Campus, is Assistant Editor of Neurology Alert.
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