MD - Doctor of Medicine Central Nervous System Disorders Questions and Answers — Questions and Answers
Question 1: A 68-year-old male presents with a resting tremor in his right hand, bradykinesia, and rigidity. His symptoms have progressed slowly over the past two years. Which of the following is the primary pathophysiological mechanism responsible for this patient's motor symptoms?
- Degeneration of cholinergic neurons in the nucleus basalis of Meynert
- Autoimmune demyelination of oligodendrocytes in the central nervous system
- Loss of dopaminergic neurons in the substantia nigra pars compacta (Correct answer)
- Expansion of CAG trinucleotide repeats in the huntingtin gene
Correct answer: Loss of dopaminergic neurons in the substantia nigra pars compacta
The classic motor symptoms of Parkinson's disease—tremor, rigidity, and bradykinesia—are primarily caused by the progressive loss of dopamine-producing neurons in the substantia nigra pars compacta. This leads to a dopamine deficit in the striatum, disrupting the basal ganglia motor circuit. Cholinergic neuron loss is characteristic of Alzheimer's disease. Demyelination is the hallmark of multiple sclerosis. CAG repeat expansion causes Huntington's disease.
Question 2: A 29-year-old female presents with an episode of unilateral vision loss and pain with eye movement that resolved over several weeks. Six months later, she develops numbness and tingling in her left leg. An MRI of the brain reveals multiple periventricular white matter lesions. A lumbar puncture is performed. Which cerebrospinal fluid (CSF) finding would be most supportive of a diagnosis of multiple sclerosis?
- Elevated protein with a normal cell count (albuminocytologic dissociation)
- Presence of two or more IgG oligoclonal bands not present in the serum (Correct answer)
- Low glucose, high protein, and marked neutrophilic pleocytosis
- Xanthochromia and a high red blood cell count
Correct answer: Presence of two or more IgG oligoclonal bands not present in the serum
The presence of two or more IgG oligoclonal bands in the cerebrospinal fluid that are not found in the patient's serum is a hallmark laboratory finding in multiple sclerosis, present in over 95% of patients. This indicates intrathecal (within the CNS) production of immunoglobulins, reflecting the inflammatory nature of the disease. Albuminocytologic dissociation is characteristic of Guillain-Barré syndrome. Low glucose and high neutrophils suggest bacterial meningitis. Xanthochromia points to a subarachnoid hemorrhage.
Question 3: A 75-year-old man is brought to the emergency department 90 minutes after the sudden onset of left-sided weakness and facial droop. A non-contrast head CT scan shows no evidence of intracranial hemorrhage. His blood pressure is 170/95 mmHg. What is the most appropriate immediate intervention?
- Immediate administration of high-dose aspirin
- Urgent neurosurgical consultation for hematoma evacuation
- Administration of intravenous alteplase (tPA) (Correct answer)
- Observation and supportive care with repeat CT in 24 hours
Correct answer: Administration of intravenous alteplase (tPA)
For patients with an acute ischemic stroke who present within the 3 to 4.5-hour therapeutic window and have no contraindications (like hemorrhage on CT), intravenous alteplase (a thrombolytic agent) is the standard of care to restore cerebral blood flow and improve functional outcomes. Aspirin is typically started 24 hours after tPA administration. Neurosurgical consultation would be for a hemorrhagic stroke, not an ischemic one without hemorrhage. Observation alone would miss the critical opportunity for reperfusion therapy.
Question 4: Which of the following is the fundamental pathogenic mechanism underlying Myasthenia Gravis?
- Degeneration of upper and lower motor neurons
- Antibody-mediated destruction of postsynaptic acetylcholine receptors (Correct answer)
- T-cell mediated attack on the myelin sheath of peripheral nerves
- Deposition of alpha-synuclein aggregates in motor neurons
Correct answer: Antibody-mediated destruction of postsynaptic acetylcholine receptors
Myasthenia Gravis is an autoimmune disorder characterized by the production of antibodies against components of the postsynaptic membrane at the neuromuscular junction, most commonly the nicotinic acetylcholine receptor (AChR). This leads to a reduced number of functional receptors, impairing neuromuscular transmission and causing fluctuating muscle weakness. Motor neuron degeneration is the basis of Amyotrophic Lateral Sclerosis (ALS). T-cell mediated attack on peripheral myelin is characteristic of Guillain-Barré syndrome. Alpha-synuclein is associated with Parkinson's disease.
Question 5: A 45-year-old man with a history of alcohol abuse is brought to the emergency department. He has been continuously seizing for 10 minutes despite pre-hospital administration of an IM benzodiazepine. In the ED, he remains unresponsive and continues to have generalized tonic-clonic seizure activity. After securing the airway and obtaining IV access, which medication should be administered first?
- A loading dose of oral phenytoin
- An intravenous bolus of propofol
- An intravenous infusion of phenobarbital
- An intravenous bolus of lorazepam (Correct answer)
Correct answer: An intravenous bolus of lorazepam
The first-line emergent treatment for status epilepticus is an intravenous benzodiazepine. Lorazepam is often preferred due to its rapid onset and relatively longer duration of action compared to diazepam. If seizure activity continues after adequate benzodiazepine administration, a second-line agent like fosphenytoin, levetiracetam, or valproic acid would be used. Propofol and phenobarbital are generally reserved for refractory status epilepticus that has not responded to first and second-line agents. Oral medications are not appropriate for emergent management.
Question 6: A pathologist is examining brain tissue from a patient who had severe dementia. The microscopic examination reveals numerous extracellular neuritic plaques and intracellular neurofibrillary tangles, particularly in the hippocampus and neocortex. These findings are the classic neuropathological hallmarks of which condition?
- Lewy Body Dementia
- Creutzfeldt-Jakob Disease
- Huntington's Disease
- Alzheimer's Disease (Correct answer)
Correct answer: Alzheimer's Disease
The two cardinal neuropathological lesions that define Alzheimer's Disease are extracellular plaques composed of beta-amyloid peptide and intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein. Lewy Body Dementia is characterized by alpha-synuclein aggregates (Lewy bodies). Creutzfeldt-Jakob disease shows spongiform changes and prion protein deposition. Huntington's disease is characterized by neuronal loss and gliosis in the caudate and putamen due to mutant huntingtin protein.
MD - Doctor of Medicine Central Nervous System Disorders Questions and Answers
A 68-year-old male presents with a resting tremor in his right hand, bradykinesia, and rigidity.
His symptoms have progressed slowly over the past two years.
Which of the following is the primary pathophysiological mechanism responsible for this patient's motor symptoms?