By Will Boggs MD

NEW YORK (Reuters Health) - A spiral series of self-sustaining cycles of excitation underlies the puzzling condition known geographic tongue, physicists suggest.

"Geographic tongue" refers to the red patches that appear when filiform papillae on the tongue are lost (they subsequently regrow). The condition affects about 2% of the population, but its exact cause is unknown.

"Utilizing a dynamical systems approach (i.e., a mathematical description of the dynamical aspect of the condition) allows one to get an insight regarding the evolution and severity of the geographic tongue (GT) condition," Dr. Gabriel Seiden from Weizmann Institute of Science's Department of Earth and Planetary Sciences in Rehovot, Israel, told Reuters Health by email. "I hope that by combining our theoretical approach to GT with medical research we might better understand the underlying mechanism/cause of this intriguing medical condition."

Dr. Seiden and Dr. Sofia Curland from Max Planck Institute for the Physics of Complex Systems in Dresden, Germany, saw similarities between the dynamic appearance of the tongue with phenomena observed in such excitable media as forest fires, cardiac arrhythmias, chemically driven reaction-diffusion systems, and morphogenesis in multicellular organisms.

Seeking to explain GT in terms of excitable media dynamics, they viewed GT dynamics as an evolution between a healed (rest) state, a highly inflamed (excited) state, and a healing (recovering) state.

According to their cellular automaton model, propagation of spiral patterns results in a continuous, self-sustaining excitation of recovering regions, which can force the epithelium through successive reentry cycles of rest and excitation before it can settle back into its stable, healed state.

This model, detailed in the March issue of the New Journal of Physics, would account for the presence of multiple lesions of different sizes expanding on the epithelium simultaneously and merging upon contact, thus leading to highly irregular patterns.

"From a theoretical point of view, patterns with closed boundaries (i.e., circular or oblate) will in general keep their shape as they expand throughout the tongue, unless there is some obstacle/inhomogeneity in the epithelium," Dr. Seiden said. "Thus, if such patterns are observed on the tongue of a GT patient it is most likely that the tongue will be gradually affected and subsequently healed."

"Open ended patterns -- in particular spirals -- tend to be self-sustaining and thus, from a theoretical point of view, will linger for longer periods of time," he said. "We do not know exactly how spiral patterns form in GT patients (due to lack of careful clinical studies on the initiation and evolution of different patterns). In other excitable media, however, these patterns commonly result from inhomogeneities in the medium or due to external intervention."


New J Phys 2015.