Bradykinesia

Bradykinesia is a medical term used to describe slowness in movement. The term bradykinesia is often used to encompass various hypokinetic motor disturbances, including akinesia, which refers to a complete absence of movement, and hypokinesia, which refers to the reduced amplitude of movement, such as small handwriting or walking with a shuffling gait.

Bradykinesia typically occurs in individuals with Parkinson disease, a movement disorder where the dopamine-producing neurons in the substantia nigra of the brain undergo degeneration. The substantia nigra is a part of the basal ganglia, a collection of brain regions that control movement through their connections with the motor cortex. Bradykinesia is also a symptom of other movement disorders, such as Lewy body dementia, multiple system atrophy, and progressive supranuclear palsy. These disorders are collectively called atypical parkinsonism or “Parkinson-plus” syndromes because they display characteristics of Parkinson disease along with additional clinical features. Finally, bradykinesia may be a side effect of medication, including antipsychotics such as haloperidol, which blocks dopamine receptors; and metoclopramide, a dopamine antagonist, used to treat vomiting.

Bradykinesia can manifest in several different ways, such as difficulty with repetitive tasks, like tapping fingers or clapping hands; a reduction of automatic movements, such as blinking the eyes or swinging of the arms when walking; and difficulty initiating movements, such as standing up or turning in bed. Progressive bradykinesia may lead to freezing, a pause in movement common when walking and at thresholds (i.e., crossing a door frame or entering an elevator). Generalized bradykinesia may also lead to the appearance of unnatural stillness or decreased facial expression, a condition known as hypomimia. 

Bradykinesia is diagnosed when an individual has difficulty performing rapidly alternating movements, such as tapping the finger and thumb together, rotating the palms up and down, or tapping the foot up and down. Individuals with bradykinesia typically show a decrease in speed or amplitude of movement in addition to slowness, which helps to differentiate bradykinesia from other disorders that may lead to difficulty in repeated alternating movements, such as cerebellar ataxia. 

The bradykinesia-akinesia incoordination test (BRAIN) is a keyboard-tapping task used to assess upper limb motor function in individuals with movement disorders. The BRAIN test involves tapping the keys “S” and “;” on the keyboard with alternating fingers as rapidly as possible for 30 seconds. Individuals with bradykinesia may be unable to complete this task or do so slower than expected. 

The diagnosis of Parkinson disease requires the presence of bradykinesia in addition to other typical symptoms, such as tremors, rigidity, or postural instability. Ruling out other potential causes of motor dysfunction, like medications, is also necessary for diagnosis.

Treatment of bradykinesia depends on the underlying cause. In individuals with Parkinson disease, treatment focuses on increasing the amount of dopamine signaling in the brain. This can be done by administering levodopa; a precursor molecule converted into dopamine by a decarboxylase enzyme. Levodopa is often administered along with a peripheral decarboxylase inhibitor called carbidopa, which decreases the conversion of levodopa to dopamine in the peripheral circulation, thereby allowing a higher concentration of it to enter the brain. Levodopa/carbidopa is usually the first-line treatment for Parkinson disease and is particularly effective at controlling motor symptoms like bradykinesia. However, its effectiveness can decrease over time, individuals can develop motor fluctuations, and symptoms may begin to reappear. In such cases, treatment involves increasing the frequency of levodopa/carbidopa medications or adding another group of medications that aim to increase dopamine levels by preventing its peripheral degradation (e.g., COMT-inhibitors, like tolcapone and entacapone, and MAO-B inhibitors, like selegiline).

An alternative to levodopa/carbidopa is dopamine agonists (e.g., bromocriptine, cabergoline, apomorphine, pramipexole, ropinirole), which stimulate dopamine receptors in the brain. These medications are not as effective as levodopa/carbidopa. They tend to have severe side effects, such as nausea, dizziness, headaches, vomiting, orthostatic hypotension, cardiac arrhythmias, or decreased impulse control and compulsive behaviors (e.g., uncontrolled shopping, gambling, and hypersexuality). Finally, anticholinergic medications, such as benztropine, may be used when the motor symptoms are predominantly tremor or rigidity; however, they are not as effective for bradykinesia.

In cases where medications are ineffective at controlling the symptoms, a surgical treatment called deep brain stimulation can be conducted. Deep brain stimulation involves an implantable device that sends electrical impulses to the brain's basal ganglia, which improves dopamine’s effects in the brain for those with Parkinson’s disease.

Individuals with bradykinesia caused by atypical parkinsonism may also benefit from the same treatment strategies as Parkinson’s disease, though effectiveness may vary depending on the disorder's characteristics. Finally, in cases where bradykinesia is a side effect of medication, withholding the offending medication can generally resolve the symptoms. 

Bradykinesia refers to slowness in movement and is one of the main motor symptoms of Parkinson’s disease, a movement disorder caused by decreased dopamine signaling in the brain. Bradykinesia may occur in other movement disorders, like Lewy dementia, multiple system atrophy, and progressive supranuclear palsy, as well as a side effect of antidopaminergic medications, like haloperidol or metoclopramide. Treating bradykinesia may include increasing brain dopamine levels in individuals with parkinsonism or suspending the offending medication, depending on the underlying cause.