Four Myths About Visual Snow

Four Myths About Visual Snow

Here is the video and a short summary of Professor Peter Goadsby’s presentation at the 2018 Visual Snow Conference event. Goadsby discusses the history of Visual Snow and some myths about the condition.

Visual Snow Conference

In total there are five presentations from the Visual Snow Conference that I have chosen to write about. I recommend that you read about them/watch the videos in this order. The first two are more general, the last three go into more complex detail. If you have already seen some of the videos I recommend that you watch them again anyway, as it is easy to miss certain details.

1. Four Myths About Visual Snow (Peter Goadsby)

2. Visual Snow And Sensory Misperception (Owen White)

3. Behavioural Research Into Visual Snow (Joanne Fielding)

4. The Origins Of Visual Snow (James T. Fulton)

5. Visual Snow And Visual Pathways (Viktoria Pelak)

* These are not necessarily the presentation titles the authors used at the event

Four Myths

Goadsby says that when he first mentioned Visual Snow to his colleagues they were not interested. The main reason for this was a belief that the condition did not actually exist. This was because there was a lack of objective evidence for its existence, with only reports coming from patients.

The patients describing this condition were often perceived as being slightly “crazy”, and what they described was actually believed to be a type of migraine, due to illicit drug use, or their anxiety/emotion. HPPD and Persistent Migraine with Aura were of course more well-known conditions.

Effectively there were four myths that Goadsby didn’t believe in and set out to disprove:

1. That Visual Snow does not exist

2. That the patients describing it are crazy (emotions/anxiety as a cause)

3. That Visual Snow is a form of migraine

4. That Visual Snow is always caused by illicit drug use

Visual Snow Exists (And It's Not Crazy)

One of the reasons for Goadsby to have believed that Visual Snow did in fact exist was that people more or less described it in the same way, including children. With initial information from 10 years of patients that he’d received (2001-2011), Goadsby was able to work out some of common themes, and then test them out on a larger group of patients.

He says that there was some variation among patients but he stresses that they had to establish a core group that was similar. So the eventual clinical classification ended up excluding some symptoms and patients.

This is not to say that those exclusions (such as illicit drug-induced Visual Snow) bear no relevance. The intention he says was to expand the core group gradually, because at that stage they simply wanted to prove that Visual Snow did exist.

They came up with working criteria going forwards:

  • Visual snow as a continuous pan-field disturbance which is dynamic.
  • Patients should have one out of four additional core symptoms: palinopsia, photophobia, enhanced entoptic phenomena( e.g. floaters), impaired night vision.
  • Symptoms should not be from “drug abuse”, of ophthalmological origin, and not consistent with migraine aura.
 

This was the theoretical definition to Visual Snow that they needed at the time. However in order to provide the objective proof that Visual Snow was real they used brain imaging. They found that their core group had altered brain function: a hypermetabolism in the lingual vision cortex. The significance of this area for the condition is an open question he says, but it demonstrated that Visual Snow is real.

By now thousands of people have described Visual Snow in studies, the clinical criteria has expanded, and more academic researchers have begun to look at Visual Snow.

Visual Snow Is A Distinct Condition

Goadsby says that the first paper that seemed to mention Visual Snow in 1995 also talked about migraine – which was problematic. Differential diagnoses have historically been persistent migraine aura, post-hallucinogenic drugs, and anxiety/emotion.
 
In terms of migraine Goadsby says that there was an association in the sense that those with Visual Snow often also have migraine and are comorbid. But he does not believe that those with migraine are more likely to have Visual Snow. Rather there is an interaction between the two and those with migraine are more likely to notice Visual Snow if they have it. This (in my opinion) may also be the cause for the other two differential diagnoses.

Goadsby says that cortical spreading depression and aura observed in migraine involve characteristic changes in cerebral blood flow that were not seen in those with Visual Snow. Those with migraine see fortification spectra (scintillating scotoma) and this is different from the characteristic static in Visual Snow. I myself do not generally experience migraine although I have on very rare occasions observed scotoma. The image below demonstrates what they look like.

Scintillating scotoma are not Visual Snow
Fortification Spectra: This is not Visual Snow

More recently Goadsby has been able to gather information from a set of 1000 patients with visual snow, he presents the statistics in the video. Some of the findings from this survey are that the common onset is at 13 years of age, there is generally a stepwise worsening, and most attribute no apparent cause.

The Video

Play Video

My Thoughts

Goadsby and his research partners have done a lot of good for the recognition of Visual Snow, and the progress of research. It is very important to be aware of the myths and misconceptions surrounding Visual Snow as it can lead to unnecessary prescriptions and create false stigma – the consequences of which can themselves be enormous, particularly for children as Goadsby remarked.

An interesting point were the drawings of children and how they showed Visual Snow. The thought of it is unpleasant but it is a way to recognise if somebody has/had Visual Snow at a young age.

Goadsby’s educated opinion that those with migraine experience an interaction with their Visual Snow suggests that there would also perhaps be other conditions that interact with Visual Snow. Treating those may in the current state of affairs be a feasible route towards indirect improvements.

It is also important to appreciate respectfully how long this progress has taken and that there is still a fairly long road ahead. Survey data for example is good but it needs to be meaningfully constructed and interpreted.

Links

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