AssessmentsMovement disorders: Pathology review
USMLE® Step 1 style questions USMLE
A 12-year-old boy is brought to the pediatrician by his parents due to personality changes, difficulty speaking, and impaired balance over the past year. They describe the patient as a previously bright, cheerful child who enjoyed activities at school and socializing with friends. Over the last several months, he has become very impulsive and irritable and is also having significant trouble completing homework on time. The patient also used to be an avid soccer player but recently dropped out of the team due to poor performance and lack of interest. Vitals are within normal limits. Physical examination of the patient shows significant loss of coordination and dysarthric speech. Slit-lamp examination of the eyes is shown below:
Reproduced from: Wikimedia Commons
Which of the following additional findings is most likely to be found in this patient on further testing?
Content Reviewers:Yifan Xiao, MD
In the neurology ward, there’s a mother with her child, named Justin, who is 2 years old. Justin’s mother is worried because she palpated a mass in his abdomen while bathing him. Justin also has been having episodes of rapid, dancing eye movements as well as shocklike, jerky movements of his extremities. Next, there’s a 42 year old male, named Oliver. For the past few months, Oliver has been acting strangely according to his sister. He forgets important information and is very aggressive with his family. He also has bursts of wild, dance-like movements of his arms. His sister is very anxious because their father died at age 50 after having similar symptoms. Okay, now next to Oliver, there’s a 58 year old male, named Ashton. His wife has noticed that her husband’s face has become inexpressive and he has been having hand tremor at rest for the past few months. Also, his movements have become slower, and he had frequent falls. His medical history is otherwise insignificant.
Okay, so all of them have movement disorders. The cerebrum, cerebellum, and basal ganglia all help coordinate movements, so movement disorders can be traced back to these structures. Movement disorders can be broadly grouped into 2 categories, hypokinetic disorders, which cause slowness of movement, and hyperkinetic disorders, which cause excessive involuntary movement.
Alright, when it comes to hypokinetic disorders, a lot of their symptoms are grouped together under the term “parkinsonism.” This can appear in many conditions including Parkinson’s disease itself, and other syndromes called “parkinson-plus” syndromes. These cause parkinsonism, plus other clinical features. Some Parkinson-plus syndromes include Lewy body dementia, multiple system atrophy, and progressive supranuclear palsy.
Okay, the four cardinal symptoms of parkinsonism can be remembered with the mnemonic “TRAP”. “T” for tremor, which is classically described as a resting, pill-rolling tremor, because it looks like someone is rolling a pill between their thumb and index finger. “R” stands for rigidity, which is often described as a cogwheel-like rigidity. This means that when attempting to passively move a limb, there are a series of stops or stalls, kind of like a cog on a wheel. There’s also lead-pipe rigidity, which is when a limb is rigid throughout the entire passive movement, kind of like trying to move a lead-pipe. “A” stands for akinesia, which is the absence of movement, and is a severe form of the more common finding of bradykinesia, which is slowness of movement. This can manifest as a narrow-based shuffling gait or a decreased facial expression, almost to the point where the individual’s face looks like they’re wearing a mask. “P” stands for postural instability, which causes a stooped posture, problems with balance, and an increased frequency of falls. Usually, these symptoms are asymmetric, with the exception of medication-induced parkinsonism, which usually causes symmetric symptoms.
Now, Parkinson’s disease is a slowly progressive genetic disorder that primarily affects individuals over 50 years old. Parkinson’s derives from the loss of dopamine-producing, or dopaminergic, neurons in the substantia nigra, which is a part of the basal ganglia. The substantia nigra can be split into two sub-regions, the pars reticulata, and the pars compacta. The pars compacta sends messages to the striatum via neurons rich in the neurotransmitter dopamine, forming the nigrostriatal pathway, which helps to stimulate the cerebral cortex and initiate movement.
In Parkinson’s the pigmented dopaminergic neurons in the pars compacta gradually disappear and this depigmented region can be seen in an autopsy. There’s also degeneration in the nigrostriatal pathway which decreases its projections to the cortex, thus causing bradykinesia.
Under a microscope, Lewy bodies are present in the substantia nigra, and these are eosinophilic, round inclusions made of alpha-synuclein protein, that are present in the dopaminergic neurons befor