Distal Arm Weakness

Distal arm weakness may be caused by involvement of the intrinsic hand muscles (interossi, thenar and hypothenar muscles, lumbricals) or extrinsic hand muscles (long finger flexors and extensors). ALS is typical for the former type, and IBM is typical for the latter type. Incoordination of skilled finger movement due to cerebellar disease is associated with normal strength. Poor mobility due to joints pain and swelling should not be confused with muscle weakness. Mononeuropathies such as ulnar, radial, median, and AIN,lesions usually cause differential loss of function. Myasthenia sometimes causes weakness of the wrist and finger extensors. A small but distinct group of distal hereditary myopathies should always be borne in mind. Progressive sensorimotor neuropathies are usually associated with sensory symptoms. Multifocal motor neuropathy can be a diagnostic challenge.