Hodak J, Fischer U, Bassetti CLA, Schankin CJ. Episodic
Visual Snow Associated With Migraine Attacks. JAMA Neurol. 2019 Nov 25. doi:10.1001/jamaneurol.2019.4050. [Epub ahead of print]
Visual snow syndrome (VSS) is a debilitating disorder
characterized by continuous visual snow (VS), ie, tiny flickering dots in the
entire visual field resembling the view of a badly tuned analog television,
plus additional visual symptoms, such as photophobia and palinopsia. There is a
high comorbidity with migraine and migraine aura. To our knowledge, this is the
first report of patients with an episodic form of VS (eVS), strictly
co-occurring with migraine attacks.
Methods
Between January 2016 and December 2017, we saw 3 patients
with eVS and 1934 patients with migraine at our tertiary outpatient headache
center. Diagnoses were made according to the International Headache Society
International Classification of Headache Disorders-32 and our previous work,
except for the requirement of permanence for VS. The case series was approved
by the Cantonal Ethics Committee Bern (Req-2017-00698) with waiver of written
informed consent based on general consent given by all patients.
Results
The 3 patients presented initially for headache as chief
complaint. They denied VS outside migraine attacks and did not report
additional visual symptoms suggestive of VSS during headache except for
photophobia. Neurological examination and magnetic resonance imaging results
were normal.
Patients experienced black and white (2 patients) or black
and yellow (1 patient) eVS during migraine attacks, nonfluctuating in
distribution and severity. Episodes lasted from less than 2 minutes before and
during the attack in 1 patient to during the entire migraine attack in 2
patients.
Discussion
Three patients report episodes of VS exclusively at the
beginning or during migraine attacks. The description was identical and matched
the definition of VS in VSS except for not being continuous. In the
syndrome-defining study, only patients with continuous VS were included,
impeding the identification of an episodic form. Based on the present case
series, we propose to distinguish between VSS, a debilitating disorder
characterized by continuous VS and additional visual symptoms persisting over
years, and eVS, an uncommon self-limiting symptom during migraine attacks.
The relationship between migraine and VSS is still
unresolved. Although the severity of VS in VSS does not fluctuate in parallel
to the migraine cycle, the strict co-occurrence of eVS and migraine reported
here epitomizes a close proximity. This is in agreement with the clinical
picture of migraine being a disorder of sensory processing and VSS being a
disorder of visual processing and also with neuroimaging showing overlapping
dysfunctional areas in the visual association cortex.
Episodic VS is uncommon given that only 3 of 1934 patients
with migraine (<0.2%) were identified despite asking routinely for visual
symptoms. It was remarkably linked to migraine attacks and occurred without the
additional symptoms found in VSS. In the
first patient, the occurrence prior to headache attacks might suggest an aura
phenomenon. However, the history of migraine without aura in all patients, the
brief duration in 1 patient and long duration in 2 patients, the affection of
the entire visual field, and the lack of directed movement speak against a
cortical spreading depressionlike mechanism6 and thus against eVS being an aura
symptom. In clinical practice, a detailed history in patients reporting visual
flickering is therefore necessary to differentiate aura from eVS. This is
important because the diagnosis of aura might have implications for patient
guidance on contraception or timing of triptan intake.
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