When the impact of skin diseases on the lives of those it affects usually is considered a "cosmetic problem." The most common autoimmune disease known as alopecia areata is an example of the lack of attention on skin diseases. The pathobiology of the disease and available therapies are disappointing, according to a recent study.
In the New England Journal of Medicine, scientists offer a review of the clinical presentation, pathogenesis, and management of alopecia areata and provide relevant background information about the biologic and path biologic features of the hair follicle. As of now, evidence suggests that the disease is considered a T cell-mediated autoimmune disease where the gradual loss of protection usually provided by immune privilege of the normal hair follicle plays an important role.
Affecting an estimated 4.5 million people in the United States, alopecia areata is the most frequent cause of inflammation-induced hair loss. It can affects children and adults of all hair colors. Close to 66-percent of those affected are younger than 30 years old. The disease is generally not sex related, but in a study of 226 Chinese patients who were 16 with a median age of onset at 10 years old, the male-female ratio was 1.4:1. The disease was proven to be more severe in boys and those who developed the disease early in life.
Normal Hair Growth
Scientists believe it is important to understand normal hair growth and the normal immunobiology of the hair follicle to understand the changes that occur in alopecia areata. Hair follicles are the only organs in the body that have lifelong, extensive, cyclic transformation. They switch from a rapid growth to a short phase of organ involution. Then the hair follicle enters a relative quiescence before it reenters the cycle. The regenerative cycle is caused by an abundance of melanocyte stem cells and keratinocyte.
Clinical Presentation and Diagnosis
Alopecia areata is the loss of hair in well-circumscribed patches of normal-appearing skin, mostly on the scalp. The onset is rapid and can progress to the point where all the hair can be lost on the scalp or even the entire body. There are different variants of the disorder including ophiasis, when hair loss affects the occipital scalp; "sudden graying," where pigmented hair follicles are attacked with grey hairs; and diffuse forms of alopecia. These descriptions along with clinical signs like cadaver hairs, nail pitting, exclamation-mark hairs, and the growth of white hair in alopecic lesions can lead to the correct diagnosis of the disease.
Treatment is not typically easy for alopecia areata. Curative therapy is nonexistent. Some physicians rely on the high rate of spontaneous remission and often recommend a wig if it does not occur because current therapies are unsatisfying. The best tested immunosuppressive treatment is intradermal infections of triamcinolone acetonide given every 2 to 6 weeks. It stimulates localized re-growth in 60 percent of cases.
Improved pathobiologic concepts may ultimately pave the way to better management and outcomes in alopecia areata. Because of inflammation-induced dystrophy of the follicle, the hair shaft can no longer be firmly anchored in the hair canal and is rapidly shed, but the follicle can retain its capacity to regenerate and continue cycling sincle stem cells are not destroyed. Therefore, hair loss is reversible.
The main therapeutic challenge is to reduce the already established inflammatory infiltrates and to prevent recurrence and spread to previously unaffected hair follicles. Unfortunately, current therapies do not meet this challenge. Scientists believe a better understanding is needed of how the perifollicular infiltrate in alopecia areata develops and why it forms around follicles.
The development of the disease is strongly genetic. Patients with a family history of alopecia areata also have a history of atopy, Down's syndrome, or other autoimmune diseases. In a genome wide association study of 20 families with alopecia areata, Martinez-Mir identified at least four susceptibility loci on chromosomes 6, 10, 16, and 18. On chromosome 6, one susceptibility locus was found at 6p, a site that corresponds to the HLA locus; a second locus was found at 6q23.3, a site that is outside the HLA gene cluster. The region on chromosome 16 overlaps with a region near a susceptibility locus for Crohn's disease. The susceptibility locus for alopecia areata on chromosome 18p also contains a psoriasis-susceptibility region, showing that alopecia areata can coexist with psoriasis.
Current pathobiologic concepts may inform preclinical research to develop better therapeutic options for alopecia areata. Scientists believe if treatment focuses on restoring or preventing the collapse of hair follicle immune privilege, then more effective management of the disease will prevail. New therapeutic strategies are being studied in preclinical research.