Mar 8 2007
"This shouldn't preclude transporting a patient from point A to point B in an aircraft, but this concern does need to register as a legitimate risk for a small number of patients. Personnel ought to know how to guard against it."
A case report published in the current issue of the journal Prehospital Emergency Care suggests that light streaming through whirling helicopter rotor blades during medical air transport can cause symptoms ranging from nausea to full-blown seizures in a very small number of patients. The report, published in the January/March volume, cites several studies, case reports and historical examples related to photosensitive epilepsy, suggesting that the phenomenon is an under-recognized but highly preventable complication of helicopter transport.
"This shouldn't preclude transporting a patient from point A to point B in an aircraft," said Jeremy Cushman, M.D., an Emergency Medicine attending physician at the University of Rochester Medical Center and the report's lead author. "But this concern does need to register as a legitimate risk for a small number of patients. Personnel ought to know how to guard against it."
The case report details an account of a patient who suffered a severe foot injury and required an airlift from a remote geographic location to a hospital in Baltimore, where Cushman worked at the time. Flight paramedics noted flickering bursts of sunlight cast across the patient's face, to which the patient's eyes soon began blinking, and then his facial muscles began jerking in coordinated rhythm. The patient, stable and displaying strong vital signs, immediately fell into a seizure, despite paramedics' attempts to block the flashes from the patient's face.
During the hospital examination, the patient reported no previous head injury or family history of seizures; he also had a normal EEG and CT scan, and, at a three-month follow-up visit, reported no recurrence of the seizure.
"He was not diagnosed with a seizure disorder," Cushman said. "But we never exposed him to flickering light again, either, giving us all the more reason to suspect that as the cause."
Giuseppe Erba, M.D., professor of Neurology and Pediatrics at the University of Rochester Medical Center, is a world expert on photosensitivity, including epileptic seizures caused by flashing lights of video games and television. Erba says that he also encounters patients affected by a similar flickering effect caused by sunlight filtering through a row of trees as the patients are riding in cars.
"Photosensitive patients may twitch, then jerk, and finally, if nothing is done to stop it, have a seizure," Erba said. "It's a tricky business, this photosensitivity, because it can exist without a patient having spontaneous seizures, as the paper states. This makes prevention even more difficult, especially since routine EEG tests are not always carried out properly in the lab and too often, false negative results occur."
Cushman and co-author Douglas Floccare, M.D., M.P.H., of the Maryland State Police Aviation Command researched how often this sort of light-induced epilepsy occurs in patients, even pilots, with no history of seizures – especially in aircraft on sunny days. The team found several photosensitive epilepsy studies and various reports from over the course of decades, even centuries, both on ground and in flight. Together, these pieces create a picture that suggests the condition may be more common and difficult to diagnose than originally thought.
For instance, Cushman highlights second century writings from the Roman novelist and orator Apuleius, who noted that the spinning of a potter's wheel could send onlookers into seizures. Cushman also describes an array of other non-whirling stimuli that have been documented over time to induce seizures, including music, hot water, working with fractions, and even tooth brushing.
The most common photosensitive stimulus is television, Cushman said, and resulting seizures are often dubbed instances of "video game" or "space invader" epilepsy, a condition that Erba studies and has made recommendations to help prevent.
"Almost 10 years ago in Japan, more than 700 children were hospitalized after watching a cartoon explosion on a show called Pokemon," Cushman said. "And with numbers like that, there's more at play than the mere two in 10,000 patients that statistics show are vulnerable to light-induced epilepsy. We've begun to wonder if even people not diagnosed with epilepsy can also be affected, to some degree, by a flickering stimulus like the light in our report."
Cushman noted that other studies further underscore the more widespread photosensitivity evidenced by the Pokemon cartoon incident; one showed that even 28 percent of normal, non-epileptic control subjects exposed to light flashes can suffer symptoms such as nausea, headaches, fear and vomiting, if the flickering light is set to the right frequency. In that same study, as many as 5 percent of "normal" subjects experienced a loss of consciousness or seized.
Convinced that photosensitivity triggered by spinning rotors, though rare, is an under-recognized and preventable complication of medical air transport – one that can be produced even in some patients without previous seizure history – Cushman now instructs flight paramedics to routinely shield patients' eyes while en route.
"More than 30 years ago, there was a case reported of a young soldier waiting to board a helicopter who began seizing without any previous medical history," Cushman said. "Other reports exist for incapacitation of Air Force pilots, with anything from simple spatial disorientation to serious seizures. What's interesting is that these findings were reported for previously healthy individuals."
He and Floccare use the term "flicker illness" to refer to the whole continuum of complications, from wooziness to vomiting to all-out seizing, induced by quick-flashing light.
"Many aircraft commonly used for air medical transport have similar frequencies to the 24 flickers per second of the rotor blades in the helicopter used in the case we highlight," Cushman said. "And though this isn't so common a complication – I've seen four total cases in the course of five years and thousands of transports – the more I dialogue with others, the more they recall having encountered something similar."
Cushman noted that the report may be more relevant in sunnier places like Phoenix, where colleagues have been very interested in the report. Baltimore and Rochester see some 105 and 61 sunny days per year on average, respectively, compared to aptly named Phoenix's 211.