Hypermetria

Hypermetria is a neurological sign defined by an abnormal increase in the amplitude of voluntary movements, resulting in overshoot of the intended target. It is a form of dysmetria commonly produced by cerebellar dysfunction, particularly involving the cerebellar hemispheres or their connections, though it can appear with broader cerebellar or brainstem involvement.

Etiology and pathophysiology: Hypermetria arises from impaired cerebellar processing of limb dynamics and predictive motor control, leading to errors in movement scaling and timing. It often accompanies other cerebellar signs such as intention tremor, dysdiadochokinesia, ataxia, and gait disturbances. Causes include acute lesions (stroke, trauma), demyelinating disease, degenerative conditions (spinocerebellar ataxias), tumors, and alcohol-related cerebellar degeneration.

Clinical features: In reaching or pointing tasks, patients overshoot targets and require corrective adjustments. Hypermetria is typically observed during voluntary movements and tends to worsen with faster or longer-range movements. Proprioception is usually preserved, and the overshoot may be most evident during dynamic tasks rather than at rest. It is often discussed together with hypometria, which describes undershoot of targets.

Assessment: Diagnosis is based on neurological examination. Bedside tests such as finger-to-nose, heel-to-shin, and rapid alternating movements help demonstrate overshoot and trajectory errors. Neuroimaging (MRI or CT) can support the identification of cerebellar pathology underlying the sign.

Management and prognosis: Treatment focuses on the underlying condition. Rehabilitation through physical and occupational therapy aims to improve coordination and develop compensatory strategies. The prognosis depends on the etiology and extent of cerebellar involvement.