Psoriatic alopecia and sebaceous glands: An unfinished symphony
June 15, 2017
Every so often, patients with psoriasis would ask me about their hair loss, and I assumed that it was mechanical in nature, probably due to breakage of hair getting tangled in scales, and traumatized by pruritus. George et al, in their review of psoriatic alopecia, state that “Alopecia and other hair abnormalities occurring in patients with psoriasis were first recognized over four decades ago, yet psoriatic alopecia is not a well-known concept among clinicians.” I am embarrassed to admit that I am one of those clinicians. It’s time appreciate the presentations of psoriatic alopecia — although much remains to be learned of its pathogenesis.
In a retrospective review of 33 scalp biopsies on 31 patients having histopathologic diagnosis of psoriasis belonging to 31 patients, alopecia was a presenting feature in 48% of cases. The most common follicular-related changes were infundibular dilatation (87%) followed by perifollicular fibrosis (77%), perifollicular lymphocytic inflammation (68%), thinning of the follicular infundibulum (55%), and fibrous tracts (28%). Of interest, sebaceous glands were absent in 60% and atrophic in 25% of cases (2).
Alopecia may occur within the plaque itself; it is usually non-scarring and improves with therapy. Scarring may occur in the context of secondary infection. Psoriatic alopecia may also appear as a generalized telogen effluvium, be associated with alopecia areata, or be due to medication, notably methotrexate or retinoids. Increasingly, there have been reports of psoriatic alopecia secondary to TNF-alpha inhibitors (1).
TNF-alpha inhibitors may yield psoriatic alopecia in the context of their paradoxical reaction of causing (or exacerbating) psoriasis, regardless of whether prescribed for psoriasis, rheumatoid arthritis or Crohn disease. In most cases, alopecia in psoriatic patients improves with standard therapy (such as topical steroids) or upon discontinuation of the inducing medication.
One of the major intrigues is trying to decipher what role the sebaceous gland has in this process. Liakou et al, performing histological and stereological analyses of involved and healthy skin of 14 psoriatic patients were able to demonstrate a significant reduction of the number of sebaceous glands and the volume of the individual glands themselves. The authors speculated that the sebocytes may not differentiate properly in psoriasis, and may play a role in the pathogenesis of psoriasis and psoriatic alopecia (3). In a transcriptome study of lesional psoriatic skin versus normal skin, Rittié et al found that a coexpressed gene module (N5) enriched 11.5-fold for lipid biosynthetic genes. They also observed fewer visible hairs in psoriatic skin, compared with uninvolved nonlesional psoriatic skin or normal skin (P < 0.0001). Sebaceous glands were markedly atrophic in psoriatic versus nonlesional psoriatic skin with a 91% average reduction in volume. These results suggested that loss of visible hair in psoriasis may result from abnormal sebaceous gland function. (4)
As stated earlier, there have been an increasing number of reports of TNF-associated psoriatic alopecia Afanasiev et al reported 3 cases in middle-aged women, with histories of either Crohn disease or inflammatory arthritis, but without a prior history of psoriasis. Two patients received adalimumab and one infliximab. All 3 developed psoriatic plaques in the scalp with alopecia, after a variable length of time of being on TNF-inhibitors, ranging from 4 months to 3 years. Each patient improved after discontinuing the TNF inhibitor. Histologically, marked atrophy of the sebaceous glands was observed. A re-biopsy of the scalp in one of the patients showed regrowth of the sebaceous lobules upon stopping the TNF inhibitor therapy. The authors concluded that atrophy of sebaceous lobules is a potentially reversible, characteristic and conspicuous feature of tumor necrosis factor inhibitor-associated psoriatic alopecia; this may be distinguished from idiopathic psoriatic alopecia by the clinical history of drug exposure and sometimes by the histologic presence of a mixed inflammatory response including plasma cells and eosinophils. (5).
The role of the sebaceous gland in psoriatic alopecia is speculative. Perhaps there is a mechanical component, in that drier hair may be more brittle and subject to trauma. The sebaceous gland is located just superior to the bulge area that harbors hair follicle stem cells; could it be that diminution of the sebaceous gland has some bearing on the regenerative capability of the hair follicle? Much remains to be learned about the relationship of the sebaceous gland with psoriatic alopecia. Until such time, patients may be reassured that their alopecia will likely improve with topical treatments, and/or removal of the offending agent.
1. George SMC, et al. Psoriatic alopecia. Clin Exp Dermatol 2014; 40: 717-21.
2. Silva CY, et al. Psoriatic alopecia – fact or fiction? A clinicohistologic reappraisal. Indian J Dermatol Venereol Leprol 2012; 78: 611-9.
3. Liakou AI, et al. Marked reduction of the number and individual volume of sebaceous glands in psoriatic lesions. Dermatology 2016; 232: 415-24.
4. Rittié L, et al. Sebaceous gland atrophy in psoriasis: An explanation for psoriatic alopecia. J Invest Dermatol 2016; 136: 1792-1800.
5. Afaasiev OK, et al. TNF-inhibitor associated psoriatic alopecia.: Diagnostic utility of sebaceous lobule atrophy. J Cutan Pathol 2017; 44: 563-9.
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