Case Study - An unusual case of unequal pupils

It is important to identify the cause of any neurological signs, explains Dr Zara Aziz.

The patient’s pupils were unequal in size (Photograph: SPL)

Mr S was a 52-year-old man who reported that his wife had noticed his right pupil was more dilated than the left. This had concerned her as he had presented with left-sided facial weakness and unequal pupils three years earlier following a transient ischaemic attack (TIA).

He had been living in the Caribbean at the time and remembered that a CT scan of his brain had been normal, though an MRI scan of his neck had shown some slight abnormality.

He felt that the left side of his forehead had never been 'quite the same' since the TIA. He was not hypertensive and his current medications included a statin and aspirin. He was a long-term smoker of about 10 cigarettes a day.

Clinical examination
On clinical examination he was well with no motor weakness or sensory deficits. Tone and tendon reflexes were normal. His BP was 130/76mm Hg with a regular pulse of 76bpm. His visual acuity was normal when corrected by his spectacles and his fields were intact. There was no deficiency of eye movements or evidence of ptosis.

His pupils were unequal in size, the right being more dilated. However, they were both reactive to light and accommodation, although the left pupil was slow to dilate in darkness.

Medical history revealed that Mr S had an internal carotid artery dissection (ICAD)while in the Caribbean. There had been no evidence of microemboli at the time and he had therefore been treated conservatively with aspirin for anticoagulation. A follow-up MRI scan had been carried out six months later and revealed a normal internal carotid artery.

Mr S was reassured though kept under close review, and advised to report any further problems.

In the absence of any other neurological signs, it was likely that Mr S had now presented with a long-standing left small pupil, which had led to an impression of a dilated right pupil. The diagnosis was Horner's syndrome.

Horner's syndrome includes ptosis of the upper and lower eyelids, ipsilateral constricted pupil and/or ipsilateral anhidrosis (loss of sweating). The clinical signs depend on the location of the lesion on the sympathetic pathway.

In recent years, ICAD has been identified as an important cause of Horner's syndrome.

It is thought that dissection causes inflammation, which stretches (or damages) the pericarotid sympathetic area.

This has previously been underdiagnosed due to lack of accurate imaging techniques. MRI is now the gold standard for looking at carotid arteries.

Underlying cause
ICAD can occur spontaneously or from minor trauma, such as from coughing or weightlifting. This is thought to be from hyperextension, rotation or full flexion of the neck.

It is a recognised cause of ischaemic stroke in young people. Neck pain can also be a clinical feature in many of these patients.

Most ischaemic events arise within seven days of the dissection, although it can be a few months. Treatment is usually with heparin and then warfarin, or antiplatelet therapy.

ICAD is an important diagnosis to consider in patients presenting with Horner's syndrome. It is necessary to seek neurological advice and/or make urgent hospital referral for further investigations if this is suspected.

  • Dr Aziz is a GP in Bristol

Lucas C, Moulin T, Deplanque D et al. Stroke patterns of Internal Carotid Artery Dissection in 40 patients. Stroke 1998; 29: 2646-8.

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