Wednesday, March 18, 2020

Visual snow and migraine

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.

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.

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.

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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