A 55-year-old man presents with a right sided rest tremor and slowness of movement.
A year ago he noticed that he could not smell his food. He has not had any falls and his eye movements are
normal. His past medical history is unremarkable and he does not take any medication.
Which of the following structures is most likely to be most affected?
A Left cerebellar hemisphere
B Left cerebral neocortex
C Olfactory nerve
D Red nucleus
E Substantia nigra This is the correct answer
The diagnosis is most likely idiopathic Parkinson’s disease.
The patient has a pre-motor symptom of olfactory disturbance and fulfils the UK-PDS brain bank criteria for
Parkinson’s disease. He is developing motor symptoms due to loss of more than 50% of the dopaminergic
neurones in the substantia nigra.
Option A is incorrect because there are no cerebellar signs (he has normal eye movements and no
nystagmus).
Option B is incorrect as lesions of the outermost layer of the cerebral cortex present with problems of memory,
attention and consciousness.
Option C is incorrect as isolated lesions of the olfactory nerve would not present with tremor.
Option D is incorrect as the red nucleus is responsible for motor coordination of the upper arm and shoulder.
Loss of dopaminergic neurones in the substantia nigra is predominantly responsible for the symptoms in
Parkinson’s disease.