As part of our podiatry training, anatomy of the foot and leg features consistently. Muscle origins, insertions and actions are a common part of our anatomical knowledge. As someone with a dermatological bias, I often thin that skin anatomy is not often covered in sufficient detail and many podiatrists unaware of the intricacies of the skin, particularly when studying dermatological disease as anatomy can sometimes explain dermatological patterns.
An example is seen in figure 1. A patient with a rash on the lateral side of the foot. To many, it’s a diagnosis of tinea or eczema but examining this further, so many rashes on the plantar surface are limited to this invisible border, infrequently, crossing this point towards the dorsum of the foot.
Hugh Wallace
This has been noticed and reported on previously. The observation is credited to Dr Hugh J Wallace [1909-1985] (figure 2), who was the lead Consultant Dermatologist (appointed in 1951), at St John’s Hospital for Diseases of the Skin in London [1].
Wallace's line
Wallace had noticed and documented how many types of skin eruptions on the sole ended abruptly at the edge of the plantar surface creating an apparent line of delineation. It was latterly coined as ”Wallace’s line” by Harper and Copeman in 1983 in a poster exhibited at the British Association of Dermatologists meeting [2].
Harper and Copeman discussed how many conditions such as pompholyx and lichen planus rarely crossed Wallace’s line. They proposed the line represented a surface feature created by the underlying changes in anatomy of plantar to dorsal skin (changes including pigmentary, sweat glands, hair and dermatoglyphic alterations) [3]. Vascular differences were also noted above and below the line [4].
Latterly, Payne and Branfoot [5] proposed that the line reflected a drastic change in the lymphatic drainage exemplified by the fact that bruising and venous ulceration extending from the ankle never appeared to cross this line. Changes in the pattern of lymphatic drainage may affect the presentation of a range of diseases.
Subsequently, the term “Wallace’s line” has been adopted in mainstream dermatological language since in “Rooks Textbook of Dermatology” the main reference textbook for this discipline [3]. Coincidentally, the term Wallace’s line can be applied to the border of palmar skin too.
Lines in Dermatology
As an interesting aside, dermatology is littered with many “lines”. If you are interested, I would suggest a look at this paper by Savitha in 2017 discussing lines in dermatology:
Disambiguation: For the geographers amongst us, there is another Wallace’s line. Alfred Wallace in 1859 reported a geographical border between Asia and Australia which demonstrated differences in the species of animals above and below it. Read it here.
References
1. Anon., Obituaries files. British Journal of Dermatology, 1985. 112(2): p. 241-245.
2. Harper, J.L. and P.W. Copeman, Wallace's line - What is it? British Journal of Dermatology, 1983. 24: p. 24.
3. Copeman, P.W.M., Wallace's line. British Journal of Dermatology, 1987. 116(4): p. 607-607.
4. Bernhard, J.D., A.R. Rhodes, and J.W. Melski, Wallace's Line in serum sickness and Kawasaki disease. Br J Dermatol, 1986. 115(5): p. 640.
5. Payne, C.M.E.R. and A.C. Branfoot, Wallace's Line. British Journal of Dermatology, 1986. 114(4): p. 513-522.
6. Savitha, A.S., Lines in Dermatology. Clinical Dermatology Review, 2017. 1(1).