History
Mr. Chan was a 70-year-old man with a history of diabetes under dietary control, hyperlipidemia, and nasopharyngeal carcinoma treated with radical chemotherapy and radiotherapy in 1999.
He presented with a 2-week history of left angle of mouth drooping that his children first pointed out. He also reported a longstanding history of slowly progressive slurred speech and swallowing difficulty for 3-5 years. There was no limb weakness.
Physical examination
Physical examination was pertinent for an upper motor neuron type left facial weakness with reduced velocity of movement.
The lower cranial nerves were normal. Dysarthria was present. Power of the 4 limbs was normal.
Investigations
The baseline blood work was unremarkable.
A plain CT of the brain demonstrated left frontal subcortical hypodensities at the anterior watershed area with associated negative mass effect as evidenced by the ex vacuo dilatation of the adjacent lateral horn of the ventricle.
ECG showed sinus rhythm. Chest X-ray was normal without cardiomegaly or mass.
Thought process
Given the uncertain acuity of symptom onset, the diagnostic dilemma was one between an acute ischemic stroke and post-radiotherapy cranial nerve palsy in the setting of prior nasopharyngeal carcinoma.
There were two aspects to consider in deducing the most plausible diagnosis. First, although non-specific and did not correspond to the left frontal lesion on CT brain, a review of the physical examination demonstrated mild left upper limb pronation with drift or overt weakness.
Second, the facial nerve is rarely implicated in direct tumor invasion and post-radiotherapy cranial nerve palsy for nasopharyngeal carcinoma due to its favorable anatomical position (running laterally from the skull base, intra-osseous course thus shielded by the temporal bone, more robust vascular supply) as opposed to the other upper and lower cranial nerves running through the cavernous sinus, superior orbital fissure, jugular foramen and hypoglossal canal.
All in all, with the strong vascular risk factors, a delayed presentation of ischemic stroke was deemed to be higher on the differential list compared to a post-radiotherapy cranial nerve palsy.
The chronic bulbar and auditory symptoms may, however, be attributable to the post-radiotherapy complications.
Next steps
Aspirin was started for secondary prevention, as was risk factor optimization. Neurovascular imaging was arranged to look for large vessel disease secondary to the post-radiotherapy complication.