MAGNETIC-RESONANCE-IMAGING OF THE FOREARM AS A DIAGNOSTIC-AID IN PATIENTS WITH SPORADIC INCLUSION-BODY MYOSITIS

Because weakness of finger flexors and atrophy of the forearms are fre quent findings in inclusion body myositis (IBM) patients, we examined the forearm muscles by MRI to determine if involvement of the distal m usculature has a characteristic diagnostic pattern. We performed MRI o f the forearms in 21 randomly selected patients with histologically co nfirmed IBM and in 9 patients with other, age-matched, neuromuscular d iseases who served as controls. In addition, we analyzed axial images of 10 individual forearm muscles blindly without knowledge of the clin ical status or diagnosis of the patients. T-1-weighted MR images showe d marbled brightness of the flexor digitorum profundus (FDP) in 20 of 21 IBM patients, of the flexor carpi ulnaris in 7, the flexor digitoru m superficialis (FDS) in 6, the flexor carpi radialis in 4, the supina tor in 3, and the brachioradialis in 1. The extensors were normal. The abnormalities of the FDP correlated with the severity but not the dur ation of the disease and in some patients preceded overt clinical sign s of FDP weakness. In contrast, the FDS was spared even late in the di sease. We conclude that selective involvement of the FDP may occur ear ly in the course of IBM and can be easily demonstrated by MRI in up to 95% of patients. Because selective FDP involvement appears to be a ve ry frequent and characteristic finding in patients with IBM, MRI of th e forearm is a useful noninvasive test in supporting the diagnosis of sporadic IBM.