Received: 23 August 1999 Revision requested: 18 October 1999 Revision received: 16 November 1999 Accepted: 19 November 1999 Abstract Objective. To analyze pe- ripheral nerves with ultrasonography (US) and magnetic resonance imag- ing (MR) in leprosy and assess the role of imaging in leprosy patients. Design and patients. Fifty-eight nerves with abnormal clinical fea- tures or electromyograms were ex- amined in 23 leprosy patients by means of gray-scale US, Doppler US and MR imaging. Image analysis in- cluded: measurement of nerve cross- sectional area; assessment of nerve structure and MR signal intensities; identification of nerve compression within osteofibrous tunnels; detec- tion of endoneural color flow signals and Gd-DTPA enhancement. Corre- lations were made with clinical find- ings and a control group of 20 sub- jects. Fourteen nerves in active re- versal reaction were followed up af- ter therapy. Results. Leprosy nerves were classi- fied into three groups based on im- aging appearance: group I consisted of 17 normal-appearing nerves; group II, of 30 enlarged nerves with fascicular abnormalities; group III, of 11 nerves with absent fascicular structure. Group II nerves were from patients subjected to reversal reac- tions; 75% of patients with group III nerves had a history of erythema no- dosum leprosum. Nerve compression in osteofibrous tunnels was identi- fied in 33% of group II and 18% of group III nerves. Doppler US and MR imaging were 74% and 92% sensitive in identifying active reac- tions, based on detection of endo- neural color flow signals, long T2 and Gd enhancement. In 64% of cases, follow-up studies showed decreased color flow and Gd uptake after steroids and decompressive surgery. Conclusions. US and MR imaging are able to detect nerves abnormali- ties in leprosy. Active reversal reac- tions are indicated by endoneural color flow signals as well as by an increased T2 signal and Gd enhance- ment. These signs would suggest rapid progression of nerve damage and a poor prognosis unless antireac- tional treatment is started. Key words Peripheral nerves · Leprosy · Ultrasonography · MR imaging Skeletal Radiol (2000) 29:142–150 © International Skeletal Society 2000 ARTICLE Carlo Martinoli Lorenzo E. Derchi Michele Bertolotto Nicola Gandolfo Stefano Bianchi Paolo Fiallo Enrico Nunzi US and MR imaging of peripheral nerves in leprosy Introduction Leprosy (Hansen disease) is a chronic infectious disease caused by Mycobacterium leprae which, in its many and various clinical forms, primarily involves the skin and nerves [1]. The disease is most common in the tropics and subtropics, but is not limited to these climates, as en- demic foci are found also in southern Europe and the United States [2]. The initial symptom of nerve involve- ment is sensory loss, which increases the frequency of minor trauma, leading to infections and eventually to C. Martinoli, M.D. · L.E. Derchi, M.D. N. Gandolfo, M.D. Department of Radiology “R”, DICMI, University of Genoa, Largo Rosanna Benzi 8, I-16132 Genoa, Italy M. Bertolotto, M.D. Department of Radiology, University of Trieste, Strada di Fiume, I-34149 Trieste, Italy S. Bianchi, M.D. Division de Radiodiagnostic. Hôpital Cantonal Huniversitaire, Rue Micheli du Crest, Geneva, Switzerland P. Fiallo, M.D. · E. Nunzi, M.D. Department of Tropical Medicine, University of Genoa, Largo Rosanna Benzi 8, I-16132 Genoa, Italy C. Martinoli, M.D. ( ✉ ) Cattedra di Radiologia “R”, Università di Genova, Largo Rosanna Benzi, 8, I-16132 Genoa, Italy