Why Are Extrapyramidal Signs Called "Extrapyramidal"?
The term "extrapyramidal" originated from early 20th century animal experiments where researchers identified descending motor pathways in the brainstem tegmentum that were anatomically separate from (i.e., "extra" or outside of) the pyramidal tracts, which convey voluntary motor commands from the cortex through the medullary pyramids to the spinal cord 1, 2.
Historical Origin of the Term
The extrapyramidal concept emerged in the late 1890s from experimental work on dogs. Researchers discovered that after bilateral transection of the pyramidal tracts, certain tegmentospinal pathways could still convey cortically-induced seizure activity to the spinal cord 1. These pathways—originating from brainstem nuclei including the reticular formation, vestibular nuclei, red nucleus, and tectum—were anatomically distinct from the pyramidal system and thus termed "extrapyramidal."
Anatomically, the human extrapyramidal system consists of six specific descending fiber collections: reticulospinal (medial and lateral), vestibulospinal (medial and lateral), rubrospinal (lateral only), and tectospinal (medial only) pathways 1.
Evolution and Misapplication of the Term
The term underwent significant conceptual drift over the subsequent decades. Clinicians and pathologists incorrectly expanded its meaning to include:
- Forebrain structures involved in motor control (particularly the basal ganglia)
- Clinical syndromes characterized by abnormal involuntary movements (parkinsonism, dystonia, chorea)
- Drug-induced movement disorders from dopamine-blocking medications 2, 3
This expansion was problematic because it represented unwarranted translation of animal experimental results to human clinical findings 2. The assumption that humans possessed a robust extrapyramidal system parallel to the pyramidal tracts—similar to other mammals—was incorrect. In reality, extrapyramidal tracts are sparse in humans compared to other mammals 1.
Clinical Usage and Current Controversy
In psychiatric and neurological practice, "extrapyramidal symptoms/signs" (EPS) became shorthand for drug-induced movement disorders, particularly those caused by antipsychotic medications 3, 4. The guidelines reference extrapyramidal features in the context of multiple system atrophy (MSA-P) and distinguish them from pyramidal signs 5.
However, modern movement disorder specialists increasingly advocate for retiring this terminology 6. The term lacks:
- Precise clinical definition (encompasses vastly different phenomena like akathisia, dystonia, parkinsonism, and tardive dyskinesia)
- Anatomical accuracy (pyramidal and extrapyramidal systems are not mutually exclusive)
- Physiologic specificity (doesn't convey the nature or severity of movement disorders)
Clinical Pitfall
The most significant pitfall is using "EPS" as a catch-all term without specifying the actual movement disorder present. When documenting or discussing movement abnormalities, use precise phenomenologic descriptors (e.g., "acute dystonia," "drug-induced parkinsonism," "akathisia") rather than the vague umbrella term "extrapyramidal signs" 6. This specificity improves clinical communication, treatment selection, and prognostic accuracy.
The term persists in medical literature primarily due to historical inertia, despite its conceptual limitations when applied to human neuroanatomy and clinical syndromes 2, 6.