LESIONS

A Guide to Localisation in Neurology

Case 18 - Double vision and jumping eyes

What is the lesion?

Let's review the symptoms first.

The acute onset raises concern for vascular lesions (infarction or haemorrhage), inflammation (e.g. demyelination) and less likely neoplasia or infection - given the lesion must be very focal, came on abruptly, and the patient is not unwell.

Vascular

A vascular cause is likely given the sudden-onset and the patient's vascular risk factors make it even more likely. A lacunar stroke could certainly fit and it is well-recognised in the region we suspect the lesion is.

However,even though this was sudden-onset which might make it feel likely to be vascular, it doesn't have to be. It's worth considering two facts. Firstly, diplopia is always 'sudden-onset' because people either see one or two images. Secondly, the brainstem is so tightly packed that even a small lesion can cause multiple effects at onset. Hence diplopia and brainstem disease will often 'look vascular' in this sense even if the lesion is something non-vascular - what's informative is what happens next, as various other aetiologies may evolve as the lesion expands, whereas a small vascular lesion often doesn't. We don't have the luxury of time here as the patient presented the day of onset!

Inflammation is very possible here - INO is a very common feature in multiple sclerosis (MS) as well as other brainstem-involving inflammatory disorders - such as neuromyelitis optica, MOG antibody disease and Behçet's (which frequently involves the midbrain). The MLF is a heavily myelinated tract, so a common target for demyelination.

There are various infections that can affect the brainstem. Some forms of encephalitis have a particular tendency to do this, including those due to Listeria, enterovirus and Lyme disease, producing features such as cranial nerve palsy and ataxia, though usually with other features including encephalopathy. Infectious masses such as abscess and tuberculoma can affect the brainstem too. Infection is perhaps less likely in this case and there are no additional markers of it.

Toxic/metabolic causes of eye movement disorder and nystagmus exist, most prominently Wernicke’s - which features brainstem damage, particularly around the dorsal midbrain. However, this patient’s signs are focal and lateralised and he lacks the other features of this such as confusion and ataxia - though these aren't always present. We wouldn't expect such a unilateral presentation in most metabolic disorders - however, in Wernicke's the ophthalmoplegia can include unilateral findings such as VI palsy or conjugate gaze paralysis, so symmetry is not absolutely necessary. In general, with new onset nystagmus and ophthalmoplegia, Wernicke's should always cross our minds, even in no obvious risk factors (alcoholism, malnutrition)- but other causes seem more likely here.

The pons is also an important site from a metabolic perspective as osmotic demyelination can damage it - for example from rapidly-corrected hyponatraemia, liver or renal failure or diabetic emergencies. Horizontal gaze paresis can arise as part of the syndrome and in the most extreme cases people become 'locked in', with tetraplegia, anarthria and only vertical eye movements possible (allowing communication). However, there is nothing in the history to suggest any risk factors for this insult.

Tumours in and around the fourth ventricle can sometimes compress the dorsal pons with consequences such as facial colliculus syndrome, though not usually so abruptly. They are a consideration here however, and are very dangerous - fourth ventricular obstruction can lead to hydrocephalus and rapid, life-threatening deterioration.

This presentation is likely to be vascular - due to a small lacunar stroke or perhaps a small haemorrhage into the pons. Inflammation is the next possibility and imaging is needed to confirm which this is.