Substantia nigra degeneration — MRCPsych Paper A MCQ

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EasyNeuroanatomySubstantia nigra degenerationMRCPsych Paper A

A 70-year-old man has bradykinesia, rigidity and a resting tremor. Post-mortem examination shows neuronal loss in a pigmented nucleus of the midbrain. Which structure has undergone the characteristic degeneration?

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Correct answer: A — Substantia nigra pars compacta

The correct answer is A, substantia nigra pars compacta. Bradykinesia, rigidity and resting tremor constitute a characteristic parkinsonian motor syndrome. Parkinson disease is associated with degeneration of neuromelanin-containing dopaminergic neurons in the substantia nigra pars compacta, reducing dopaminergic input to the striatum. The nucleus basalis of Meynert is a cholinergic forebrain nucleus prominently affected in Alzheimer disease. Mammillary-body damage is associated particularly with thiamine deficiency and Korsakoff syndrome. The suprachiasmatic nucleus regulates circadian rhythms, while the cerebellar dentate nucleus contributes to coordination; lesions there are more likely to cause ataxia or dysmetria than a classic parkinsonian syndrome.

Reference: Seiler JL, Zhuang X, Nelson AB, Lerner TN. Dopamine across timescales and cell types: Relevance for phenotypes in Parkinson's disease progression. Experimental Neurology. 2024;374:114693. https://pubmed.ncbi.nlm.nih.gov/38242300/