What does Extra-pyramidal mean?
The brain exerts Motor control via two types of pathways:
The Pyramidal is a direct type of pathway. It starts in the cortex and through a long axon passes all the way through the Internal Capsule, decusating (85%) at the Medulla and then down the spinal cord. In the spinal cord it synapses with the lower motor neuron, which goes on to innervate muscles. Hence it is a mono-synaptic system (i.e. only one synapse occurs in-between the cortex to muscle connection) .
The Extrapyramidal on the other hand is polysynaptic and more complex, it is involved in modulating movements and controls things such as coordination, timing, force, start, end of movements etc. A number of nuclei within the brain are involved in this extrapyramidal system and these include:
- Corpus striatum: Lentiform nucleus (Putamen + Globus Pallidus) and Neo-striatum (Putamen + Caudate)
- Substania nigra
- Subthalmic nucleus
- Red nucleus
- Reticular formation of the mesencephlon
- The Cerebellum is also involved
What are Extrapyramidal Symptoms and Side Effects then?
Extrapyramidal symptoms (EPS) and side effects (EPSE) arise as a result of a disturbance to the function of the extra-pyramidal system (i.e motor control, timing, force etc). If this disturbance happens because of a disease process (for example Parkinson’s Disease or Lewy Body Dementia etc.), the are termed as Extrapyramidal symptoms. If this happens as an adverse effect of medications they are termed as Extrapyramidal Side effects. These include the following:
- Acute dystonia: Earliest to appear; there is simultaneous contraction of opposing muscles (agonist and antagonist muscles) causing posturing and slowing twisting movements. Examples include Torticollis and oculo-gyric crisis.
- Parkinsonism: Similar to Parkinson’s disease symptoms (as the same brain nuclei are involved) i.e Bradykinesia, Ataxia, Rigidity, tremor
- Tardive Dyskinesias: Tardive means slow, the movements are repetitive, involuntary and purposeless. These include; grimacing, lip smacking, lip puckering and pouting, excess blinking and tongue movements.
- Akathesia: Motor restlessness, the person cannot stay still, there is a constant desire to move e.g putting the left leg on top of the right and then vice versa repeatedly in a short time span.
Extrapyramidal symptoms / side effects occur mostly due to dopamine blockage in the Extrapyramidal system. Antipsychotics are the main class of drugs which have this effect. These are not the only type of side effects caused by anti-psychotic medications as anti-psychotics exert effects on other receptors as well such as Muscarinic, Histaminic, alpha-adrenergic etc.