Imagine seeing jagged lines, red and yellow pinwheels, and shimmering arcs invading your vision out of the blue. For many migraine sufferers, these disturbing visual symptoms are common warning signs of an imminent migraine attack. This visual phenomenon is known as visual migraine aura and affects approximately 28% of people who experience migraines . Though these symptoms can be understandably disturbing, they are typically only present for less than an hour before and after a migraine . However, for a small percentage of this population, migraine aura can last for hours, days, weeks, even years following an attack. This rare disorder is known as Persistent Aura Without Infarction (PAWOI) and the exact cause of these symptoms continues to elude researchers .
According to the International Headache Society, PAWOI is distinguished from normal migraines by having aura lasting longer than seven days . Also, these symptoms must not be related to a stroke (an infarction), tumor, or any other structural alteration in brain tissue that can be seen from an MRI or CT scan. Furthermore, they should not be related to issues affecting the eyes themselves. Electroencephalogram (EEG) results, which directly measure cortical neural activity, should also be normal, which would suggest that the symptoms are not related to epilepsy . Visual symptoms are often quite varied, and can include flashing lights, sensitivity to light, scintillating scotomas (depicted in the first image of this article), and geometric shapes [3, 5, 6]. Rarely, increased frequency and duration of afterimages, also known as palinopsia, and changes in the perception of the size of objects can occur . Though these symptoms are distracting, they do not interfere significantly with the individual’s ability to see their environment. Some people with PAWOI experience non-visual symptoms as well, which include numbness, tingling, dizziness, and tinnitus (ringing in the ears). These non-visual symptoms are also seen with regular migraine aura. PAWOI appears to affect men and women equally, and people of all different ages can experience these symptoms, from 11 year olds to 70 year olds [6, 7].
It continues to remain a mystery. Numerous case studies of this disorder have been published, yet no studies have delved into examining the mechanism behind this disorder directly. Some potential explanations have been postulated, based primarily on what is already known about migraines in general, as well as the drug treatments that have been successful with some cases of PAWOI . Due to the variety of visual symptoms, many different areas of the brain are thought to be involved . The primary explanation for PAWOI is cortical spreading depression [3, 4, 7]. Cortical spreading depression involves a wave depolarization spreading across a region of the cortex, principally in the visual cortex of the occipital lobe, followed by an inhibitory wave. These waves are implicated in regular migraines with aura but it is believed that in people with PAWOI, these waves are sustained and repeated . The brains of people with PAWOI may also be more susceptible to cortical spreading depression . Furthermore, alterations in energy metabolism has been implicated, based on Positron Emission Tomography (PET) scans finding that blood flow changes often occur in the occipital lobe during migraine attacks that involve aura . Generally, this involves a decrease in blood flow in the affected areas, like the occipital lobe of the brain . Changes in magnesium levels, increased sensitivity of NMDA receptors to the excitatory neurotransmitter glutamate, and decreased activity of the inhibitory neurotransmitter GABA have also been suggested to be involved with the pathogenesis of PAWOI .
A variety of treatments have been suggested for PAWOI, but the success has been highly variable . What works in one patient may not necessarily work in the next. Typical migraine medications have been used, as well as many anticonvulsants, such as lamotrigine, topiramate, and valproate which act primarily through blocking sodium channels and increasing GABA activity . A variety of other categories of drugs have been used as well, such as cyproheptadine, which blocks the action of the transmitters acetylcholine and serotonin and was particularly successful in one patient with PAWOI ; nimodipine, which blocks certain calcium channels; acetazolamide, a drug that blocks the activity of the enzyme carbonic anhydrase that is involved with acid-base balance in the blood, and furosemide, a drug that blocks GABA . Some cases also appear to resolve spontaneously .
Though certain cases do resolve themselves without treatment, there are others where the visual symptoms are essentially permanent. A particular subtype of PAWOI, called visual snow, is a generally permanent form of PAWOI . Those who suffer from this particular type of PAWOI have very specific and similar symptoms, which is why they are grouped together. Their main symptom, unsurprisingly, is visual snow, which involves flickering lights in their visual field that look like static on a television screen [8, 9]. Patients can also experience afterimages and trails, in which objects are “seen” even after the person is no longer focused on them, halos around lights especially at night, photosensitivity, and tinnitus (a ringing or buzzing in the ears) [8, 9]. What distinguishes this subtype from other cases of PAWOI is that people who have not had migraines can develop this condition . Even with these people, though, it is likely related to migraine, due to the presence of normal MRIs, CT scans, and ophthalmological exams, like in other PAWOI cases . Treatment, minus a few cases, is generally unsuccessful, and has involved the use of drugs that are used for other PAWOI cases, such as anticonvulsants and migraine medication [8, 9].
PAWOI is a very unique disorder and a very difficult one to study due to the fact that there are typically no problems found with traditional imaging techniques. Further research will hopefully focus on investigating groups of PAWOI affected individuals rather than just analyzing case studies. A better understanding of the cause of the condition and a potential treatment would ideally result from this, providing comfort to the people who have this disorder that, though not necessarily disabling, causes a significant amount of distress for those affected.
1. Walter F. Stewart, Martha S. Linet, David D. Celentano, Mark Van Natta, and Dewey Ziegler. “Age- and sex-specific incidence rates of migraine with and without visual aura.” American Journal of Epidemology 15 (1991): 1111-1120.
2. Michele Viana, Till Sprenger, Michaela Andelova, and Peter J. Goadsby. “The typical duration of migraine aura: A systematic review.” Cephalalgia 33 (2013): 483-490.
3. Klaus Podoll, Markus Dahlem, and David C. Haas. “Persistent migraine aura without infarction – a detailed description.” Migraine Aura Foundation, 2005.
4. O.D. San-Juan and P.F. Zermeño. “Migraine with persistent aura in a Mexican patient: case report and review of the literature.” Cephalalgia 27 (2007): 456-460.
5. G.T. Liu, N.J. Schatz, S.L. Galetta, N.J. Volpe, F. Skobieranda, and G.S. Kosmorsky. “Persistent positive visual phenomena in migraine.” Neurology 45 (1995): 664-668.
6. David C. Haas. “Prolonged Migraine Aura Status.” Annals of Neurology 11 (1982): 197-199.
7. Roldao Faleiro de Almeida, Ines Alice Teixeira Leao, Joao Bosco Lima Gomes, Ariovaldo Alberto da Silva Jr., and Antonio Lucio Teixeira. “Migraine with Persistent Visual Aura: Response to Furosemide.” Clinics (Sao Paulo) 64 (2009): 375-376.
8. John Gever. “‘Visual Snow’ Callled real, Not Drug Related.” Medpage Today, 2012.
9. Eye on Vision Foundation. “Visual Snow.” EOV, 2013.
Image Credit: Helmut Hickersberger (Own work) [CC-BY-SA-2.5], via Wikipedia Commons