Anterolateral leg alopecia: An example of a new dermatologic statistic — seen but unrecognized

By Warren R. Heymann, MD
March 4, 2020
Vol. 2, No. 9

Aside from my family, my two greatest passions in life are dermatology and baseball. There is an infinite amount to learn in each discipline — for wisdom in each I turn to Bill James (two different people). Most of you are familiar with Bill James, who was deservedly honored by the AAD in 2019 with the title “Master Dermatologist.” The baseball Bill James is the father of sabermetrics (Society for American Baseball Research-metrics), now commonly known as “analytics,” which has consumed the sport as depicted in Moneyball. The game is no longer just BA (Batting Average), RBI (Runs Batted In), or ERA (Earned Run Average). Current fans now deal with OPS (On-base Plus Slugging), WAR (Win Above Replacement), and FIP (Fielding Independent Pitching), among others. In dermatology, I would like to add another — SBU (Seen But Underrecognized). In this category, so-called “anterolateral leg alopecia” (ALA, aka peroneal alopecia) might lead the league.

Periodically over the years, several male patients noticed that they have lost hair along the sides of the lower extremities. I was unaware that this condition had a title, nor could I give anyone an adequate explanation. I would just shrug my shoulders and mumble a banality to the effect that I see this quite a bit, and don’t know what to make of it. I was intrigued by the article by Shetty et al detailing the case of a 35-year-old man with a history of male pattern baldness and chronic inflammatory demyelinating polyneuropathy who noticed sharply defined nonscarring alopecia bilaterally on the anterolateral legs of approximately 3 months’ duration. A skin biopsy demonstrated a lack of hair follicles. (1)

The first mention of ALA has been cited in the article by Danforth reviewing hair distributions, where it is stated that hairs “terminate abruptly along a transverse line just below the calf and an oblique line from without inward across the front of the leg. Kidd noticed the latter arrangement and attributed it to ‘use inheritance’ due to tight fitting shoes of ancestral generations.” (2) I have no idea what that means.

From my perspective, the first accurate depiction of ALA was called “patterned alopecia about the calves” as described by Ronchese and Chace in 1939, stating: “While the hair is supposed to cover the entire leg of a normally hairy man, one often sees hairy men with a more or less sharply outlined area of alopecia on the outer and posterior aspect of each leg…Occasionally a few hairs are present, but no stumps of broken hair can be seen or palpated.” In their assessment of 100 men aged 20 to 68 years, they found ALA in 35%, noting that in men about 40 years old, patterned alopecia was the rule, and at age 20, the exception. (3) The disorder has also been described in women. (4)

Theories regarding the pathogenesis of ALA abound ranging from leg crossing, trouser-rubbing, friction, an association with androgenetic alopecia, associated autoimmunity, or as a variant of normal. No theory has been substantiated. ALA is believed to be benign and nonprogressive. Spontaneous resolution has been reported. (5) (In the absence of any follicles, how can there be spontaneous resolution? Perhaps these cases were misdiagnosed as ALA but were really alopecia areata.) There is no literature describing effective treatment for ALA; management focuses on patient education and reassurance. (6)

I suspect that 80 years ago, Ronchese and Chase were correct presuming that ALA is a benign, patterned alopecia. But why? Could there be a neurogenic influence? Cutaneous nerves may exert trophic effects on hair follicle development, growth, and/or cycling. (7) Meralgia paresthetica, a common affliction of the lateral femoral cutaneous nerve (a sensory branch of the lumbar plexus) has been associated with nonscarring alopecia overlying and demarcation the areas of paresthesias of the lateral thighs. (8) As I was researching this commentary, I took a look at my own calves, and indeed, I am afflicted with a mild case of ALA. I am healthy, and I usually sit with my legs crossed. Indeed, when I examined my legs, pressure erythema was evident. Could years of repeated pressure locally affect neuropeptides and hairs secondarily?

In conclusion, ALA is SBU. Despite our ignorance, at the very least, it is always comforting to inform patients of their exact diagnosis and what to expect. As fascinating as it is, ALA is a benign process; I doubt that ALA will generate research funding to explore its pathogenesis.

Point to Remember: Anterolateral leg alopecia is a common condition of men that may easily go unrecognized. For concerned patients, providing an accurate diagnosis and offering reassurance is the order of the day. 

Our Expert’s Viewpoint

William D James, MD
Paul R. Gross Professor of Dermatology
Director of Education
Perelman School of Medicine at the University of Pennsylvania

In his typically humorous, but always insightful manner, Warren Heymann illuminates us on the history of anterolateral leg alopecia (ALA — not porphyria-related!). I agree this is one of those curiosities we see and reassure patients about, but don’t report. I became fascinated with pigmentary demarcation lines (a somewhat akin entity, benign and not often reported) early in my career (James WD, Carter JM, Rodman OG. Pigmentary demarcation lines: A population survey. J Am Acad Dermatol 1987; 16 (3 Pt 1): 584-590). In pursuing the incidence of these in newborns and pregnant women (1), I also learned about a variety of common skin findings in these populations I likely would not have encountered otherwise. The absence of follicles in the biopsy reported by Shetty et al deserves more investigation; other affected patients might have 4 mm punch biopsies cut horizontally to ensure there is not simply a paucity of follicles. Patients have a need to know about their concerns and having a name such as ALA aids in reassurance. Finally, it is my privilege to be able to access Warren’s prodigious expanse of wisdom when my own patient’s needs escape me.

1. Shetty VM, Pai SB, Pai K, Jenson JJ. Anterolateral leg alopecia: Unknown entity or yet underreported? Int J Dermatol 2019; 58: 1088-1089.

2. Danforth CH. Studies on hair, with special reference to hypertrichosis. IV Regional characteristics of human hair. Arch Dermatol Syphilol 1925; 12: 76-94.

3. Ronchese F, Chase RR. Patterned alopecia about the calves and its apparent lack of significance. Arch Dermatol Syphilol 1939; 40: 416-421.

4. Gupta SN, Shaw JC. Anterolateral leg alopecia revisited. Cutis 2002; 70: 215-216.

5. Sriunivas SM, Sacchidanand S, Jagannathan B. Anterolateral leg alopecia. Int J Trichol 2016; 8: 49-50.

6. Siah TW, Harries MJ. Anterolateral leg alopecia: Common but commonly ignored. Int J Trichol 2014; 6: 75-76.

7. Botchkarev VA, Peters EM, Botchkareva NV, Maurer M, Paus. Hair cycle-dependent changes in adrenergic skin innervation, and hair growth modulation by adrenergic drugs. J Invest Dermatol 1999; 113: 878-887.

8. Aranoff S, Levy HB, Tuchman AJ, Daras M. Alopecia in meralgia paresthetica. J Am Acad Dermatol 1985; 176-178.