The relation between migraine, typical migraine aura and "visual snow"

Objective: To assess the relationship between the phenotype of the "visual snow" syndrome, comorbid migraine, and typical migraine aura on a clinical basis and using functional brain imaging.

Background: Patients with "visual snow" suffer from continuous TV-static-like tiny flickering dots in the entire visual field. Most patients describe a syndrome with additional visual symptoms of the following categories: palinopsia ("afterimages" and "trailing"), entopic phenomena arising from the optic apparatus itself (floaters, blue field entoptic phenomenon, photopsia, self-light of the eye), photophobia, nyctalopia (impaired night vision), as well as the non-visual symptom tinnitus. The high prevalence of migraine and typical migraine aura in this population has led to the assumption that "visual snow" is caused by persistent migraine aura. Due to the lack of objective measures, alternative diagnoses are malingering or a psychogenic disorder.

Methods: (1) The prevalence of additional visual symptoms, tinnitus, and comorbid migraine as well as typical migraine aura was assessed in a prospective semi-structured telephone interview of patients with "visual snow." Correlations were calculated using standard statistics with P < .05 being considered statistically significant. (2) Areas with increased brain metabolism in a group of "visual snow" patients in comparison to healthy controls were identified using [(18) F]-2-fluoro-2-deoxy-D-glucose positron emission tomography and statistical parametric mapping (SPM8 with whole brain analysis; statistical significance was defined by P < .001 uncorrected for multiple comparisons).

Results: (1) Of 120 patients with "visual snow," 70 patients also had migraine and 37 had typical migraine aura. Having comorbid migraine was associated with an increased likelihood of having palinopsia (odds ratio [OR] 2.8; P = .04 for "afterimages" and OR 2.6; P = .01 for "trailing"), spontaneous photopsia (OR 2.9; P = .004), photophobia (OR 3.2; P = .005), nyctalopia (OR 2.7; P = .01), and tinnitus (OR 2.9; P = .006). Typical migraine aura was associated with an increased likelihood of spontaneous photopsia (OR 2.4; P = .04). (2) After adjusting for typical migraine aura, comparison of 17 "visual snow" patients with 17 age and gender matched controls showed brain hypermetabolism in the right lingual gyrus (Montreal Neurological Institute coordinates 16-78-5; kE = 101; ZE = 3.41; P < .001) and the left cerebellar anterior lobe adjacent to the left lingual gyrus (Montreal Neurological Institute coordinates -12-62-9; kE = 152; ZE = 3.28; P = .001).

Conclusions: -Comorbid migraine aggravates the clinical phenotype of the "visual snow" syndrome by worsening some of the additional visual symptoms and tinnitus. This might bias studies on "visual snow" by migraineurs offering study participation more likely than non-migraineurs due to a more severe clinical presentation. The independence of entoptic phenomena from comorbid migraine indicates "visual snow" is the main determinant. The hypermetabolic lingual gyrus confirms a brain dysfunction in patients with "visual snow." The metabolic pattern differs from interictal migraine with some similarities to migrainous photophobia. The findings support the view that "visual snow," migraine, and typical migraine aura are distinct syndromes with shared pathophysiological mechanisms that need to be addressed in order to develop rational treatment strategies for this disabling condition.