Physician Assistant Exam: Movement Disorders
For Physician Assistant Exam (PANCE) purposes, the four fundamental types of movement disorders are essential tremors, Parkinson’s disease, Huntington’s disease, and cerebral palsy. Different types of neurologic conditions can present with different types of problems. Some disorders, such as the peripheral neuropathies, present with a sensory type of neuropathy.
An essential tremor (kinetic tremor) is a tremor of the arm or arms, worsened with movement or any type of stressor, such as emotional stress. The essential tremor doesn’t occur all the time. Note that although an essential tremor typically involves an extremity, it can also involve other body areas, including the head. In a test question, an intermittent tremor brought on by a stressor is the key.
Here are three points about the essential tremor:
These tremors don’t occur at rest; they’re usually absent during sleep.
One effective treatment is a beta blocker, particularly propranolol (Inderal). Propranolol is lipophilic and can penetrate the blood-brain barrier.
An essential tremor doesn’t mean that the person has Parkinson’s disease. Both conditions are progressive and degenerative, but Parkinson’s has a more precise etiology and slightly different symptoms.
Parkinson’s disease on the PANCE
Parkinson’s disease (called the “shaking palsy” in 1817) is a progressive and degenerative disorder characterized by a deficiency of dopamine. Clinical manifestations include the four so-called cardinal signs: bradykinesia, pill-rolling tremor, rigidity (including lead-pipe rigidity and cogwheel rigidity), and postural instability. Parkinson’s usually presents in someone who’s middle aged.
Here are some key points concerning Parkinson’s disease:
It’s caused by a deficiency of dopamine production by the substantia nigra in the brain. The exact cause of the death of dopamine-generating cells isn’t known.
Significant muscle rigidity and ambulatory dysfunction, including a shuffling gait, can be present.
Parkinson’s disease can be associated with other conditions, some of which can affect the integrity of the autonomic nervous system — think multiple system atrophy.
The person may have a failure to thrive, and cognition problems can develop.
Treating Parkinson’s is pharmacologic. One of the big medications used is carbidopa/levodopa (Sinemet). The body changes levodopa into a synthetic dopamine. The carbidopa stops some of the metabolism of the levodopa, so the patient can receive a smaller dose.
Another medication for treating Parkinson’s is amantadine (Symmetrel), which was once used to treat influenza A. It’s no longer recommend for treating influenza B, and both the A and B viruses are now resistant to amantadine, but for Parkinson’s, this med can reduce some of the symptoms.
It may be used as monotherapy in early stage Parkinson’s, but it’s often used in combination with carbidopa/levodopa. It may work as an antagonist of the NMDA (N-methyl-D-aspartate) type glutamate receptor, which increases dopamine release and blocks reuptake of dopamine. It can help especially with bradykinesia.
Pramipexole (Mirapex), which is a dopamine agonist, can help with the tremors and dyskinesias of Parkinson’s. It can cause sleepiness.
For another important class of medications used in the treatment of Parkinson’s disease, look at the following example question.
Which class of medications is used in treating Parkinson’s disease?
The correct answer is Choice (C). Dopamine and acetylcholine normally exist in the brain in equal amounts, and the medications used in treating Parkinson’s disease can upset this balance, hence the worsening symptoms. Anticholinergics are used to help with the symptoms of Parkinson’s and to maintain a healthy balance between dopamine and acetylcholine.
As for the other choices, antipsychotics would make Parkinson’s worse, because antipsychotics antagonize dopamine. Antidiarrheals are used in treating diarrhea. Steroids are used in treating a multiple sclerosis exacerbation, and plasmapheresis is used in treating Guillain-Barré syndrome, a myasthenic crisis, and certain forms of vasculitis.
Huntington’s disease on the PANCE
Huntington’s disease is a genetic disorder that’s inherited in an autosomal dominant manner, resulting in trinucleotide CAG repeats. It’s characterized by choreiform movements, which are involuntary, irregular movements of the arms. The arms make it look like the person is dancing. In addition to chorea, Huntington’s can be associated with dystonia.
Dystonia is an involuntary movement characterized by muscle spasm. Huntington’s disease is associated with an increased mortality — the average lifespan in young adulthood is about 15 to 20 years after the onset of symptoms.
Here are some key points concerning Huntington’s disease:
This condition affects the brain and can cause confusion, psychosis, and dementia. It’s associated with a host of cognitive and psychiatric symptoms. A main symptom is depression, which may have an organic cause deriving from the effect of Huntington’s disease on the brain.
In people with Huntington’s, a leading cause of mortality is infectious, usually aspiration pneumonia. Huntington’s is also associated with cardiomyopathy, which is the second leading cause of mortality.
Huntington’s has no cure. The treatment is supportive with medications used to help the symptoms. Medications include antipsychotics and antidepressants.
Besides Huntington’s chorea, another condition that can cause choreiform movements is Sydenham’s chorea (St. Vitus’ Dance), which is associated with rheumatic fever.
Cerebral palsy on the Physician Assist Exam
Cerebral palsy is a condition that commonly affects motor function. Cerebral palsy comes in various types, and the most common type causes spastic movements. Like multiple sclerosis (MS), cerebral palsy is an upper motor neuron lesion.
Note that cerebral palsy can present with a variety of symptoms, from problems with balance to spastic movements, involuntary gesturing, and significant ambulatory dysfunction. Treatment is based on the predominant presenting symptoms.