Vitiligo & Alopecia Areata: Can they occur together?

Alopecia areata and Vitiligo are Closely Related

Alopecia areata is an autoimmune disease that causes hair loss. Vitiligo is an autoimmune disease that causes loss of pigment in the skin. The prevalence of vitiligo is estimate to be between 0.5 and 2 %. The prevalence of alopecia areata is estimate between 0.1 and 0.2 % of the population. 

Is the risk of vitiligo increased in alopecia areata?

There are studies that have reported both outcomes. For example, a 1994 study by Schallreuter and colleagues found no increased coincidence of vitiligo and alopecia areata. Nevertheless, three studies did should that patients with alopecia areata have a higher risk of developing vitiligo  however studies by Chu et al, Narita et al and Huang et al (see references below) showed that patients with alopecia areata probably do have a higher risk for developing vitiligo compared to the general population.  Overall, about 3 to 8% of alopecia areata patients have vitiligo (compared to the general prevalence of vitiligo mentioned above of 0.5 and 2 %).

Similarities of AA and Vitiligo

We have come to learn that alopecia areata and vitiligo share many similarities. Both conditions are common in children and adults. In fact, about one half of patients with vitiligo develop their condition before age 20. About one-half of those with alopecia areata develop their condition before age 20. 

Both diseases are relatively asymptomatic meaning that most patients do not have itching, burning or pain. There is inflammation in both conditions, but the amount of inflammation tends to be on the lower side. Most of the inflammation in alopecia areata and vitiligo consists of T cells: CD8+ T cells are present in the epidermis of the skin in vitiligo and in the hair follicle sheath in alopecia areata; CD4+ T cells are in the dermis.   

Both are associated with other autoimmune conditions, especially thyroid disease. The prevalence of thyroid disease has been estimated to be as high as 19.4% in those with vitiligo and 28% in those with alopecia areata.

Vitiligo and AA are TH1-diseases

Vitiligo and AA are driven more by interferon gamma (IFN-γ) signalling than TNF-α which makes one consider vitiligo and AA as so called "TH1 mediated diseases". The predominant Th1 cytokine is IFN-γ.  CD8+ T cells play a key role in alopecia areata and vitiligo and interferon is abundant in affected skin of both diseases. Vitiligo and alopecia areata appear to depend primarily on IFN-γ

Role of TNF in AA and Vitiligo

TNF-α is inflammatory cytokine. Its levels are elevated in TH17-mediated diseases and appears to be required for the diseases to occur. Psoriasis is an example of a TH17 disease and other examples include inflammatory bowel disease, and rheumatoid arthritis. These conditions require TNF-α as well as IL-17, IL-23, and IL-22.  

TNF appears less directly relevant in alopecia areata. However, some studies have suggested that TNF-α can be elevated in vitiligo and alopecia areata. Surprisingly though, treatment of patients with vitiligo and alopecia areata with TNF blocking drugs have been largely unsuccessful and sometimes treatment even triggers, flares or worsens the conditions. 

Conclusion

There are many recognized similarities between alopecia areata and vitiligo and the diseases are closer related than one might otherwise have thought. Both diseases are strongly driven by IFN-γ. Treatments that reduce IFN-γ, including JAK inhibitors, are proving useful for both diseases. Further studies of alopecia areata will likely yield some benefit for how vitiligo is ultimately treatment and vice versa. 

REFERENCE
Schallreuter KU, Lemke R, Brandt O, et al. Vitiligo and other diseases: coexistence or true association? Hamburg study on 321 patients. Dermatology. 1994;188:269–275.

Chu SY, Chen YJ, Tseng WC, et al. Comorbidity profiles among patients with alopecia areata: the importance of onset age, a nationwide population-based study. J Am Acad Dermatol. 2011;65:949–956. 

Narita T, Oiso N, Fukai K, Kabashima K, Kawada A, Suzuki T. Generalized vitiligo and associated autoimmune diseases in Japanese patients and their families. Allergology international: official journal of the Japanese Society of Allergology. 2011;60:505–508.

Huang KP, Mullangi S, Guo Y, Qureshi AA. Autoimmune, atopic, and mental health comorbid conditions associated with alopecia areata in the United States. JAMA Dermatol. 2013;149:789–794.