Horizontal double vision
Is it bilateral 6th nerve palsies or something else?
I saw a case on Monday morning with the neurology trainees that illustrates why you need to know your neuroanatomy and neurophysiology to practice neurology. You can’t delegate this bit of memory to Dr Google as you have to rehearse it whilst you examine patients.
Case
The patient was admitted from a feeder hospital with non-fatiguable horizontal double vision on looking both to the left and to the right side. She also had papilloedema. She has a history of intracranial hypertension and her lumbar puncture done the previous week had an opening pressure of 33 cm of water, which is raised. The normal CSF opening pressure is 12-18 cm of water.
I asked if the person who had done the LP had documented if the column of CSF moved up and down in the manometer when the patient breathed and if the person who had done the LP had also done Queckenstedt's manoeuvre?
As you breathe in the venous return to the heart increases, which causes the veins, venous sinuses and venous plexuses around the meninges to collapse and the CSF pressure drops. The opposite happens when you breathe out. The fluid at the top of the manometer therefore should rise and fall with respiration. If this does not happen it can indicate a spinal block, i.e. the CSF in the lumbar sac is not connected to the pressure changes in the whole of the subarachnoid sack.
Queckenstedt's manoeuvre
Hans Queckenstedt, while serving in the army in 1916, devised his test to detect spinal cord compression.
Queckenstedt described: “The narrowed [spinal] channel impedes movement of fluid with an increase in pressure above the compression site… The increment in pressure above the obstruction can be demonstrated by compression of the neck…, which produces an increase in venous blood in the cranial cavity, with concomitant reduction in space for the cerebrospinal fluid… The increased fluid pressure immediately transmitted throughout the system normally can be demonstrated with a… manometer attached to a lumbar puncture needle. In lesions of the cord the manometric change is greatly retarded.” (Quickenstedt, 1916).
In the context of intracranial hypertension, Queckenstedt's manoeuvre can provide important information about the venous drainage from the cranium. If compression of the right and/or left external jugular veins doesn’t increase the CSF pressure from reducing the venous flow from the veins and sinuses at the base of the skull it indicates that there may be a thrombosis in the jugular vein or the sigmoid sinus on a particular side; yes, Queckenstedt’s sign can be localising. If compression on both sides fails to raise the pressure then the block is likely to be in the spinal canal, which is what Queckenstedt described.
Please note the CSF pressure only increases by about 2-3cm of water with jugular vein compression, which is more than what is seen with normal inspiration and expiration at rest and about the same as seen if ask the patient to do a Valsalva manoeuvre, whilst doing the LP.
Horizontal diplopia
Make sure the diplopia is truly horizontal and there is no vertical component, i.e. if one of the images is tilted or they are above each other. If there is any vertical component then the problem is not limited to the medial or lateral rectus muscles and will involve the elevators, depressors, intortors and extortors of the eye (superior and inferior recti and inferior and superior oblique muscles).
This patients diplopia was true horizontal diplopia on extremes of gaze with the images separated by a space with the far image being blurred. This means that there was more than 6 degrees separation between the two eyes; with anything less than 6 degrees the images tend to overlap each other. You can usually tell which muscle is weak, either the medial rectus or lateral rectus when the images are separated by looking to see which eye has visible sclera. The sclera should not be visible with near-normal ABduction or ADduction. If the images are overlapping and the degree of separation is very small you need to do the alternate cover test to see which images disappear.
When you do the alternate cover test and the far and blurred image disappears this localises the weak muscle. Please note the image is blurred because the image falls on the peripheral retina and not on the macular; this is often called the false image, which is a misnomer as it is an image that is being seen albeit less clearly.
This patient had bilateral 6th nerve palsies and the alternate cover test confirmed that both the lateral recti were failing to ABduct the relevant eyes completely.
Pseudo bilateral 6th nerve palsies
Whenever you see a patient with bilateral 6th nerve palsies make sure you are not dealing with pseudo palsies from ADductor or convergence spasms. The clue to this diagnosis is that when they try and ask the patient to ABduct the eye they can't and the eye movements are associated with a rather bizarre jerky nystagmus; the nystagmus is not regular and the jerks occur at a lower frequency. The clue to the diagnosis is that the pupils are noted to constrict and the vision for distant objects will blur.
Convergence spasms occur as a result of the activation of the accommodation or triple reflex; (1) adduction of the eyes (medial recti), constriction of the pupil (constrictor pupillae) and accommodation (ciliary muscle). As a result of the accommodation reflex, the visual acuity for distant objects changes, i.e. in abduction the patient develops myopia and needs a concave lens (negative dioptres) to correct the vision.
Although convergence spasms are usually not due to "organic disease" and work-up is negative (Sarkies and Sanders, 1985), its response to botox has led some to consider it a form of dystonia (Kaczmarek, 2009). However, convergence spasms can be associated with organic pathology (Guiloff et al., 1980), for example, trauma, multiple sclerosis and other brainstem pathologies.
Please don't assume that convergence spasms are due to "hysteria" or is "functional", which is what is printed in many textbooks.
Fatigueable horizontal diplopia
Always ask if the double vision gets worse with repeated movement or tonic contraction of the involved muscle. This would indicate the possibility of myasthenia gravis, which can involve single extraocular muscles.
What is a false localising sign?
This terminology came about in the era before we had CT and MR imaging. It implies that you can’t localise the side and compartment of the pathology causing raised intracranial pressure by using the clinical sign. In this case, the bilateral 6th palsies in the presence of papilloedema are potentially false localising signs. However, you would need to exclude subarachnoid space disease and pathology of the clivus and posterior walls of the cavernous sinuses where you could potentially catch both 6th nerves with the same lesion. This patient did not have any subarachnoid space disease and the cavernous sinuses were normal, therefore, we can say in this patient the bilateral 6th nerve involvement is false localising.
YouTube Teaching
Further self-directed work/reading
Anatomy of the 6th cranial nerve, cavernous sinus, superior orbital fissure and orbit.
Examination of eye movements
How to diagnose papilloedema with an ophthalmoscope
Convergence spasms
Diagnosis and management of intracranial hypertension
How to do a lumbar puncture
General Disclaimer: Please note that the opinions expressed here are those of Professor Giovannoni and do not necessarily reflect the positions of Barts and The London School of Medicine and Dentistry nor Barts Health NHS Trust.