Movement disorders are a group of diseases and syndromes that affect the ability to control normal movement. Abnormal movements are broadly classified as either hyperkinetic (too much movement) or hypokinetic (too little movement).

Disorders Than Can Cause Abnormal Movements

There are many different disorders that can cause abnormal movements. Some of these include:

Anatomy of Movement

Movement is produced and coordinated by several interacting regions, including the motor cortices, the basal ganglia, the cerebellum, the spinal cord and peripheral neurons that then synapse on muscles. The sensory nervous system receives afferent input from the rest of the body and brings this information back to the brain in order to give the brain information about the speed and positioning of various body parts, which then allows for coordination of muscle contraction.

The Motor Cortex

The motor neuron system is divided into upper and lower divisions, based on whether they are in the central (i.e., the brain and spinal cord) or peripheral nervous system (i.e., the nerves exiting the brain stem or spinal cord that then synapse on muscles). The motor cortex initiates voluntary movements. The right motor cortex controls movements of the left side of the body, and the left motor cortex controls movements of the right side of the body. The motor cortex sends electrical signals through first order (upper) motor neurons through the basal ganglia/brain stem (explained below). These signals are subsequently passed to the spinal cord where the secondary (upper) motor neurons synapse on tertiary (lower) motor neurons, which then leave the spinal cord and synapse on their respective muscles. Once the muscles receive the electrical signal, they will contract and movement results. Diseases that affect upper or lower motor neurons can cause weakness or even paralysis of certain muscles.

Basal Ganglia

Both the cerebellum and the motor cortex send information to the basal ganglia, a set of structures deep within the brain that also help control movement. Circuits within the basal ganglia are quite complex. Within this structure, some regions communicate with each other to facilitate movement while other regions work to inhibit movement. Disruptions of these circuits have been shown to cause several distinct movement disorders. For instance, the loss of neurons in the substantia nigra in patients with Parkinson’s disease results in inhibition of movement. In contrast, nerve cell loss in the caudate nucleus, another region of the basal ganglia in patients with Huntington’s disease causes chorea. Disruptions in various regions of the basal ganglia may also cause ballism (i.e., due to infarction of the subthalamic nucleus), dystonia, tremors or tics.

Cerebellum

The cerebellum, at the base of the brain, coordinates information regarding posture and position sense (i.e., where various body parts are in space). The cerebellum processes the sensory input it receives about posture and position sense and scales movements so that they are performed precisely and with the appropriate force and speed. Cerebellar disorders can cause a variety of motor symptoms, including incoordination, tremor of their limbs, imbalance and difficulty ambulating. It is also common for cerebellar disorders to cause abnormal eye movements and speech.

Diagnosis

The diagnosis of movement disorders requires a careful medical history and a thorough physical and neurological examination. For some of these disorders, there is not a definitive clinical diagnostic test, and the diagnosis is based on the history and examination. However, brain imaging studies (e.g., magnetic resonance imaging scans) may be helpful in supporting the clinician’s suspected diagnosis. In addition, blood and urine analyses may be performed to aid in diagnosis. Genetic testing may be helpful in determining the diagnosis for some types of movement disorders.

Treatment

In order to determine the best course of treatment, it is important to determine the most likely cause of the movement abnormality. Treatment with medications can be helpful in some cases. For example, medications that replace dopamine (a chemical that occurs normally throughout the brain) can be helpful in the treatment of the motor abnormalities involved in Parkinson’s disease due to the loss of dopamine-secreting neurons in the substantia nigra. In contrast, medications that inhibit dopamine can be helpful for the treatment of some hyperkinetic disorders, such as chorea. Botulinum toxin injection into overactive muscles can be helpful in the treatment of dystonia. It is common to also include an exercise program with possible referral to physical and occupational therapy targeted at improving coordination, strength, and/or balance.