MAGNETIC-RESONANCE-IMAGING SIGNAL CHANGES IN DENERVATED MUSCLES AFTERPERIPHERAL-NERVE INJURY

THE EVALUATION OF peripheral nerve disorders has traditionally relied on a clinical history, physical examination, and electrodiagnostic stu dies. Recent studies have used magnetic resonance imaging (MRI) to eva luate a variety of both nerve and muscle disorders. In this article, w e describe the use of MRI, using short-tau inversion recovery (STIR) s equences, to evaluate muscle signal characteristics in a variety of pe ripheral nerve disorders. A total of 32 patients were studied, and 12 representative cases are discussed in detail. Increased STIR signal in muscle was seen in cases of severe axonotmetic injuries involving the transection of axons producing severe denervation changes on electrom yography. The increased STIR signal in denervated muscles was seen as early as 4 days after the onset of clinical symptoms, which is signifi cantly earlier than changes detected on electromyography. The MRI sign al changes were reversible when the recovery of motor function occurre d as a result of further muscle innervation. In cases of neurapraxic n erve injuries, characterized by conduction block without axonal loss, the STIR signal in muscle was normal, These findings show that MRI usi ng STIR sequences provides a panoramic visual representation of denerv ated muscles useful in localizing and grading the severity of peripher al nerve injury secondary to either disease or trauma. MRI using STIR sequences may therefore play an important role in the prediction of cl inical outcome and the formulation of appropriate therapy early after peripheral nerve injury.