Comment on: Is palinopsia in migraineurs an enhanced physiological phenomenon?

Dear Sir,

We read with interest the article by Kalita et al. (1). By means of a questionnaire assessment, the authors detected palinopsia in 9.8% of patients with migraine. Our group previously found a similar percentage of palinopsia in migraineurs (2). Remarkably, Kalita et al. (1) observed a much higher rate of palinopsia (57.5% of migraineurs and 12% of non-migraine controls) by mean of a different method (looking at a slide in a dark room using a smartphone at maximum illumination). In our opinion, the use of a lighted pattern does not represent an everyday source and not even an ideal source to detect palinopsia. Indeed, it is known that lighted environmental sources increase the risk of retinal after-images. If one looks at a bright object and then at a bland background, the after-image persists for about 20 seconds. The duration is related to the intensity and time of exposure to the stimulus (3).

Moreover, Kalita et al. (1) found that patients with palinopsia had more severe headaches and more frequent headaches as compared to those without palinopsia. On the contrary, in our series, patients with palinopsia had a significantly lower migraine attack frequency than those without this visual phenomenon (2). This difference is difficult to explain and further studies are warranted.

The mechanism of visual perseveration is not fully understood. Functional magnetic resonance imaging (fMRI) data showed that the onset of palinopsia is associated with activation of the occipito-temporal region of the non-dominant hemisphere, in particular activation of some connections between the parietal and occipital cortex (3). We can only speculate about the physiopathological link between palinopsia and migraine. It is noteworthy that cortical spreading depression (CSD) is known as an intrinsic electrophysiological property of central nervous systems, and although evidences supports a causal relationship between CSD and migraine aura, CSD may also be involved in migraine attacks without a “perceived” aura. Thus, it is possible that spreading depression of cortical activity is involved in the generation of visual perseveration (i.e. palinopsia) in patients with migraine when the CSD activity is confined nearby to the parietal projections of the dorsal visual pathway (3).

We strongly think that the rate of palinopsia detected with the use of a questionnaire better reflects the real clinical setting. Finally, the presence of palinopsia should be investigated in migraineurs to reassure patients experiencing such phenomenon and to avoid unnecessary diagnostic tests.