Insulin Resistance and Skin Diseases

ScientificWorldJournal. 2015;2015:479354. Epub 2015 Apr 21.
Insulin Resistance and Skin Diseases.
Napolitano M1, Megna M1, Monfrecola G1.

In medical practice, almost every clinician may encounter patients with skin disease. However, it is not always easy for physicians of all specialties to face the daily task of determining the nature and clinical implication of dermatologic manifestations. Are they confined to the skin, representing a pure dermatologic event? Or are they also markers of internal conditions relating to the patient's overall health? In this review, we will discuss the principal cutaneous conditions which have been linked to metabolic alterations. Particularly, since insulin has an important role in homeostasis and physiology of the skin, we will focus on the relationships between insulin resistance (IR) and skin diseases, analyzing strongly IR-associated conditions such as acanthosis nigricans, acne, and psoriasis, without neglecting emerging and potential scenarios as the ones represented by hidradenitis suppurativa, androgenetic alopecia, and hirsutism.

5.2. Androgenetic Alopecia

Androgenetic alopecia (AGA) is a hereditary thinning of hair induced by androgens in genetically susceptible individuals [101]. It has a polygenic pattern; the risk of AGA is known to be influenced by family history and genetic factors but precisely which gene(s) are involved is not clear [102]. In the presence of androgens, anagen phase is shortened, and hair follicles shrink or become miniaturized. With successive anagen cycles, the follicles become smaller, and short, nonpigmented vellus hairs replace thick, pigmented terminal hairs. The thinning may be diffuse, involving most of the scalp but being more marked in the frontal and parietal regions. In general, the frontal hairline is maintained with temporal recession in some women. Rarely, advanced thinning with the recession of frontal hairline occurs in virilization associated with markedly elevated circulating androgen levels [103]. Disagreements exist regarding the relationship between IR and AGA, although insulin was suggested to play a role in the regulation of cutaneous androgen metabolism and hair-growth cycle. In 2009, Nabaie et al. did not find an association between IR and AGA and suggested that IR may result from aging rather than AGA or due to the presence of metabolic syndrome [104]. Later, this was confirmed by other studies; no true association exists between AGA and IR, but their coexistence as in the case of metabolic syndrome could contribute to worsening of AGA [101]. On the other hand, Matilainen et al. reported a strikingly increased risk of hyperinsulinaemia and IR-associated disorders such as obesity, hypertension, and dyslipidemia in men with early onset of androgenetic alopecia (<35), compared with age-matched controls, supporting the hypothesis that early alopecia could be a clinical marker of IR [105]. Moreover, very recently Bakry et al. reported a significantly higher mean value of fasting serum insulin in AGA cases than in controls. Further 35% of cases and 19% of controls had IR with significant difference between both groups [106], confirming the results of previous studies which found a relationship between IR and early baldness [107–109]. Thus, a reduction in insulin sensitivity may play a pathogenetic role in the miniaturization of hair follicles, in the regulation of androgen metabolism and the hair growth cycle, all of which are relevant to the loss of scalp hair in male-pattern baldness, and [104, 109, 110] whether IR induces or promotes AGA needs to be clarified by further studies. However, it is advised that cases with early onset AGA should be assessed for components of metabolic syndrome and IR for early detection and control of cardiovascular risk factors [106].

Full study: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4419263/