Functional weakness and sensory loss

Functional weakness and sensory loss are common clinical problems with variable presentations. Functional weakness commonly presents as weakness of an entire limb, paraparesis, or hemiparesis, with observable or demonstrable inconsistencies and nonanatomic accompaniments. Documentation of limb movements during sleep, the arm drop test, the Babinski thigh-trunk test, Hoover tests, the Sonoo abductor test, and various dynamometer tests can provide useful bedside diagnostic information on functional weakness. Functional sensory loss typically affects all sensory modalities, either in a hemisensory distribution or affecting an entire limb. Although often inconsistent over serial examinations with nonanatomic features, many clinical findings reported to be helpful in diagnosing functional sensory loss are neither sensitive nor specific for functional sensory loss. The yes-no test, Bowlus-Currier test, and forced-choice tests can provide useful bedside diagnostic information on functional sensory loss. Clinicians must be prepared to make more than one diagnosis in some cases, including an organic neurological diagnosis and a diagnosis of functional overlay. Recent studies have reported relatively low rates (<5%) of misdiagnosis of functional weakness or sensory loss as indicated by subsequent diagnosis of neurological or psychiatric conditions that explained the presenting symptoms. Most neurologists find such patients more difficult to help than patients with organic disease. Management focuses on supportive psychotherapy and behavioral management, exploration of social and psychological issues, treatment of comorbid depression or anxiety, and facilitation of development of more appropriate and constructive coping methods. Many patients with functional weakness, and to a somewhat lesser extent functional sensory loss, have persisting or relapsing-remitting somatic symptoms and persistently impaired social/interpersonal, occupational, and psychological functioning.