DENERVATION HYPERTROPHY OF MUSCLE - MR FEATURES

Objective: Denervation hypertrophy is an entity well recognized in the neurology literature, but with little mention in the radiology litera ture. Denervation hypertrophy occurs when a muscle paradoxically enlar ges rather than atrophies in response to Loss of innervation. The purp ose of this report is to describe the MR appearance of true hypertroph y and pseudohypertrophy of muscle following denervation. Materials and Methods: The clinical data and MRI findings in three patients with mu scle enlargement due to denervation hypertrophy are reviewed retrospec tively. Two women and one man aged 19-80 years were included. Denervat ion resulted from spinal stenosis in one patient, a herniated thoracic disc in another, and spina bifida with a tethered cord in the third. Results: True hypertrophy of a single muscle was seen in one patient a nd pseudohypertrophy of two muscles was present in one patient. One pa tient had one muscle with true hypertrophy and one muscle with pseudoh ypertrophy. Electromyographic examination was performed and was consis tent with denervation in two patients. Biopsy confirmation of denervat ion was obtained in two patients. All five abnormal muscles exhibited increased volume, well defined margins, and normal contour. In true hy pertrophy the enlarged muscle was isointense with normal muscle on all MRI sequences. In pseudohypertrophy the MRI appearance was consistent with an excessive amount of fat interspersed throughout normal muscle . Conclusion: Magnetic resonance in these cases established muscle hyp ertrophy rather than neoplasm as the cause of a palpable mass. If musc le hypertrophy or pseudohypertrophy is seen on an MR examination of an enlarged extremity, the possibility of an underlying neurologic proce ss should be considered.