LESIONS

A Guide to Localisation in Neurology

Case 6. Headache and arm movements during pregnancy

Where is the lesion?

This patient is pregnant and has a headache. There is a differential for this and usually the cause is benign – migraine – but secondary causes do exist and are worth considering here. Three clues to a secondary cause are:

• Sudden-onset
• Focal neurological features
• Systemic illness (e.g. fever)

The headache was not sudden and the patient is well (she is also pregnant, which is an abnormal state - but this has been uncomplicated). Here however, there are focal features - involuntary movements which are lateralised. They are brief, and stereotyped - it happened the same way twice. They were also followed by a few minutes of arm weakness.

We refer to involuntary movements as hyperkinetic and there is broad a differential for these.

The movements here don't sound like tremor - the episodes were too brief, and the weakness after is not typical. They don't sound like any of the other hyperkinetic movement disorders - chorea, tic, myoclonus, dystonia - either.

They sound exactly like focal motor seizures - based on the paroxysmal nature, brief duration, involuntary jerking, and the aftermath with post-ictal weakness .

Right-sided focal motor seizures could indicate something irritating the left frontal lobe cortex. Going further, some regions of the frontal lobe have different seizure patterns (semiology), which help us localise - including:

• Simple clonic rhythmic jerking of the contralateral limb muscles in regions corresponding to the affected part of the motor homunculus (in the precentral gyrus)
• Jacksonian seizures : clonic jerking which migrates through segments of the contralateral body as the seizure focus travels along the different homuncular regions (e.g. leg -> arm -> hand)
• Tonic posturing – for example fencing or figure-of-4 postures – which can originate from the supplementary motor area (SMA)
• If the nearby language centres are involved there may be dysphasia
• Awareness and cognitive functions are sometimes affected if certain prefrontal areas are involved
• Frontal lobe seizures can be unusual and produce bilateral activity such as kicking movements resembling bicycle pedalling, with retained consciousness - which can lead to misdiagnosis of functional seizures

These sound quite simple – clonic arm and leg jerking, with retained awareness (she was able to recall and describe both attacks well, and was evidently thinking clearly enough to be able to film the second attack before it stopped).

The left primary motor cortex is likely to be involved - by some process that also causes headache. Pregnancy may well be relevant, too.

What is the lesion?