extrapyramidal

Extrapyramidal refers to the extrapyramidal motor system, a network of brain structures involved in the regulation of movement, posture, and muscle tone. It is functionally distinct from the pyramidal motor pathways and influences voluntary movement through indirect circuits linking the cerebral cortex with the brainstem, basal ganglia, thalamus, and spinal cord. Key components include the basal ganglia (caudate nucleus, putamen, globus pallidus), the substantia nigra, the subthalamic nucleus, and their connections with the red nucleus and thalamus, as well as brainstem nuclei.

Together with cerebellar and brainstem circuits, the extrapyramidal system modulates automatic and learned movements, coordinating posture, movement initiation, and muscle tone. It helps refine motor commands produced by the corticospinal tract and suppresses involuntary movements, contributing to smooth, purposeful action.

Clinical relevance: The term is often used in the context of extrapyramidal symptoms (EPS), which are drug-induced movement disorders resulting from dopamine D2 receptor antagonism in the nigrostriatal pathway. EPS include dystonia, akathisia, parkinsonism, tremor, bradykinesia, and tardive dyskinesia. EPS are commonly associated with first-generation antipsychotics but can occur with some second-generation agents and other medications.

Other diseases affecting extrapyramidal pathways include Parkinson disease, Huntington disease, progressive supranuclear palsy, and Wilson disease. Diagnosis is clinical, sometimes aided by rating scales such as the AIMS for tardive dyskinesia, the Simpson-Ayd scales for drug-induced parkinsonism, or akathisia scales.

Management focuses on reducing exposure to causative drugs when possible, using lower-risk antipsychotics, and treating symptoms with anticholinergic agents for dystonia and parkinsonism, beta-blockers or benzodiazepines for akathisia, and VMAT2 inhibitors for tardive dyskinesia. Nonpharmacologic approaches and multidisciplinary care are important for comprehensive management.