Yoga sign- An entity to remember
Cross‑legged sitting on hard uncarpeted floors for prolonged periods while meditating, eating and for leisurely social interaction is a very common cultural practice in India. Though sitting on chairs, sofas, and dining chairs are common in urban areas it is not the same in rural areas.
"Yoga sign" refers to pigmented callosities on the skin over the lateral malleoli, and at times over the fifth metatarsal and phalangeal bones due to cross‑legged sitting on hard floors which was recently described in the Indian Dermatology Online Journal.
Bony protuberances like lateral malleoli create outward pressure on the skin resulting in friction between the hard floor and the skin over it during cross‑legged sitting. Repeated shearing forces, friction, and pressure leads to hyperkeratosis which further increases pressure, creating a vicious cycle of friction, pressure, and thickening of the skin. Unlike in corns these are distributed over a much broader area (>1 cm2).
Yoga sign is often unilateral because of a dominant lateral malleolus that is subjected to more pressure friction. The authors also noted that many patients showed secondary phenomena over these sites such as lichen planus, psoriasis, and eczema in order of frequency. The authors proposed that these callosities resulting from chronic blunt injury of pressure and friction are locus minoris resistentiae (sites of less resistance) for certain dermatoses to preferentially localize over them like Koebner phenomenon.
The phenomenon could possibly be explained by the localization of resident memory T‑cells in the callosities, which are the result of repeated blunt trauma, especially in cases of lichen planus and psoriasis.
The authors saw a marked reduction in the degree of hyperkeratosis and hyperpigmentation by relieving pressure and friction using thick, soft, padding under the callosities. The authors also advise for long‑term application of 6% salicylic acid ointment and 10% urea cream daily.
While conventional treatment for secondary dermatoses is adequate even if somewhat prolonged, complete resolution of the callosities and hyperpigmentation seems an unrealistic goal.
Source- Verma SB, Wollina U. Yoga sign-A locus minoris resistentiae to remember. Indian Dermatol Online J 2021;12:760-1.