Distribution of affected muscles detected by muscle MRI.

BB = biceps brachii; TB = triceps brachii; B = brachialis; BR = brachioradialis; FCU = flexor carpi ulnaris; FCR = flexor carpi radialis; FDP = flexor digitorum profundus; FDS = flexor digitorum superficialis, FPL = flexor pollicis longus; APL = abductor pollicis longus; EP = extensor pollicis longus and brevis; ECU = extensor carpi ulnaris; ECR = extensor carpi radialis; EDC = extensor digitorum communis; P = pronator teres; S = supinator.- = normal; + mild change; ++ = mild to moderate change; +++ = moderate change; ++++ = severe change.Distribution of affected muscles detected by muscle MRI.