dysmetria

Dysmetria is a neurological sign in which there is an error in judging distance or strength of a movement, causing overshooting (hypermetria) or undershooting (hypometria) of a target. It reflects dysfunction of the cerebellum or its connections that normally calibrate limb movements. Dysmetria can affect limbs, the eyes, or the trunk and is a typical feature of cerebellar ataxia.

Causes are primarily related to cerebellar dysfunction. Acquired etiologies include stroke, traumatic brain injury, tumors, multiple sclerosis, chronic alcohol use with cerebellar degeneration, and other degenerative or inflammatory conditions that involve the cerebellum or its pathways. Congenital cerebellar abnormalities and certain metabolic disorders can also present with dysmetria.

Clinically, dysmetria is evident on targeted, voluntary movement. Patients may overshoot or undershoot when reaching for an object. On examination, finger-to-nose and heel-to-shin tests reveal misjudged movement amplitude. Other associated signs may include intention tremor, dysdiadochokinesia (impaired rapid alternating movements), and rebound phenomena. Ocular dysmetria can occur with abnormalities in saccadic or pursuit eye movements.

Pathophysiology involves disruption of the cerebellum’s ability to generate accurate feedforward control and online error correction. Lesions in the cerebellar hemispheres commonly cause limb dysmetria, while vermal damage tends to produce truncal ataxia with less precise limb control. The result is a miscalibrated movement trajectory and inappropriate end-point force.

Diagnosis is chiefly clinical, supported by neuroimaging to identify underlying lesions. Management targets the underlying cause and includes physical and occupational therapy to improve coordination, along with compensatory strategies. Pharmacologic treatment is not specific for dysmetria itself. Prognosis varies with etiology and extent of cerebellar involvement; some cases improve with treatment or resolution of the cause, others persist or progress in degenerative disease.