COORDINATION EXAM: ANATOMY
The principle area of the brain that is examined by the coordination exam is the cerebellum. The cerebellum is important for motor learning and timing of motor activity. It fine-tunes the force of agonist and antagonist muscle activity simultaneously and sequentially across multiple joints to produce smooth flowing, goal directed movements. Cerebellar dysfunction results in decomposition of movements and under and over shooting of goal directed movements (dysmetria). Decomposition of movement and dysmetria are the main elements of ataxia.
Subdivisions of the Cerebellum
The cerebellum has 3 functional subdivisions, which function as feedback and feed forward systems.
The first functional subdivision is the vestibulocerebellum. This consists of the connections between the vestibular system and the flocculonodular lobe. Dysfunction of this system results in nystagmus, truncal instability (titubation), and truncal ataxia.
The 2nd subdivision is the spinocerebellum. This system consists of the connections between the cutaneous and proprioceptive information coming from the spinal cord to the vermis and paravermis regions with corrective feedback predominantly to the muscles of truncal stability and gait. Dysfunction of this system results in gait and truncal ataxia.
Clinically, the ataxic syndromes caused by vestibulocerebellar and spinocerebellar disease are lumped together and are called midline or equilibratory (gait) ataxias. The hallmarks of these midline ataxic syndromes are truncal instability manifested by titubation (tremor of the trunk in an anterior-posterior plane at 3-4 Hz) and gait ataxia (wide based, irregular steps with lateral veering).
The 3rd subdivision of the cerebellum is the cerebrocerebellum. This system consists of connections from the cerebral cortex (predominantly motor) to the cerebellar hemispheres then back to the cerebral cortex. This system is important in motor planning. Dysfunction of the cerebellar hemispheres results in ataxia of speech (scanning dysarthria) and ataxia of the extremities (appendicular ataxia). It is important to remember that ataxia caused by disease of the cerebellar hemispheres will be ipsilateral to the dysfunctional hemisphere. The findings of appendicular ataxia are hypotonia, decomposition of movement, dysmetria, and difficulty with rapid alternating movements (dysdiadochokinesia).
The following tests of the neuro exam can be divided according to which system of the cerebellum is being examined:
Vestibulocerebellum and spinocerebellum (midline):
Rapid alternating movements
Rebound and check reflex
Although incoordination is primarily a symptom of cerebellar disease, it can also be seen from other causes such as:
a. Sensory dysfunction-loss of large myelinated sensory axons serving proprioception. This causes a sensory ataxia. Key distinguishing feature for this type of problem- a positive Romberg and loss of position sense on the sensory exam.
b. Vestibular dysfunction. Key distinguishing feature- vertigo.
c. Corticospinal tract disease can cause incoordination of the distal extremities. Key distinguishing feature- UMN signs.
Appendicular ataxia is maximum at the greatest extent and end point of the motor act so make sure you have the patient get to the full extent of the motor act when testing for ataxia.
Remember that the Romberg test is a test for position sense and not of cerebellar function.