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REHOVOT, Israel: Physicists at the Weizmann Institute of Science in Israel have clarified the intricate dynamics underpinning a tongue condition that has puzzled the medical community for decades. Known as benign migratory glossitis or geographic tongue (GT), the condition affects around 2 per cent of the global population and is characterised by evolving red patches on the surface of the tongue that may resemble a map.
The red patches appear due to loss of one of the four types of lingual papillae, tiny hair-like protrusions that cover the surface of the tongue. The affected type, called filiform papillae, is mainly distributed in the anterior two-thirds of the tongue. Despite extensive research, the exact cause of GT, a benign and mostly painless condition, remains unknown.
In their study, the researchers performed a number of numerical simulations to closely examine and visualise the development of GT, and devised a new way of identifying the severity of individual cases. “We hope these results can be used by physicians as a practical way of assessing the severity of the condition based on the characteristic patterns observed,” said lead author of the study Dr Gabriel Seiden, a researcher at the Weizmann Institute of Science in Rehovot in Israel.
The scientists approached the problem of GT as if it were an excitable medium—a spatially distributed, dynamic system with the ability to propagate signals without damping. A forest fire is a classic example of an excitable medium: it travels as a wave from its initiation point and regenerates with every tree it ignites.
This is in contrast to passive wave propagation, which is characterised by a gradual damping of the signal amplitude due to friction. However, after a wave has passed through, excitable media have to reconstitute before they can support the passing of another wave. In this way, a fire can spread through a forest, but it cannot return to a burnt spot until the vegetation has regrown.
The study found that GT can spread across the tongue in two different ways, each of which has distinguishing characteristics that could be used to diagnose severity. The researchers discovered that the condition, which typically starts as small spots on the tongue, can continue to gradually expand in circular patterns until the whole tongue becomes affected. Once affected, the tongue then heals itself. Alternatively, the condition can develop through the formation of spiral patterns. The simulations showed that these spirals evolve in regions of the tongue that are still recovering, causing re-excitation of that particular region.
“While the propagation of small circular lesions results in the whole tongue being gradually affected and subsequently healed, the propagation of spiral patterns involves a continuous, self-sustaining excitation of recovering regions, implying a more acute condition that will linger for a relatively long period of time,” Seiden explained.
Just as the development of forest fires can be strongly affected by external conditions, such as the strength of the wind, conditions surrounding the tongue may have important consequences for the dynamics of GT, according to the researchers.
In their study, they give the example of GT observed in a 1-year-old boy who developed the characteristic lesions on multiple occasions along the tongue’s edge adjacent to the growing teeth, implying that the continuous rubbing of the tongue against the gingiva may trigger the condition.
“Going forward, we intend to collaborate with physicians and dentists who treat GT patients to obtain valuable—and often scarce—empirical data regarding the dynamic evolution of the condition,” Seiden concluded. “This will allow for further, more quantitative explorations of GT, and may eventually lead to a firmer understanding of what causes the condition.”
The study, titled “The tongue as an excitable medium”, was published online in the New Journal of Physics on 31 March.
