By Gary M. White, MD
Idiopathic guttate hypomelanosis (IGH) is a benign condition in which small "white freckles" occur on the skin of the arms and legs. There is no relationship to vitiligo. Electron microscopy shows no significant structural abnormality of the melanocytes. Instead, there is a functional defect in the transfer of melanosomes from the melanocyte to the keratinocytes.
In one study [Int J Dermatol. 2011;50:798], the prevalence of IGH in patients aged ≥40 years was 87% and increased with advancing age. The sex ratio was approximately equal. The most frequent sites of involvement were the distal legs in 93%; the distal arms in 91%; the proximal arms in 73%, and the proximal legs in 58%. Thirty-nine (6%) subjects also developed IGH on the face.
Small, 2-4 mm, white macules develop on the shins and extensor arms of an adult. Some have made a distinction between IGH and macular hypomelanosis [Acta Derm Venereol. 1999;79:305-10]. Although related, macular hypomelanosis is less white and less well demarcated. There does appear to be a "hyperkeratotic" variant of IGH. These lesions are scattered, well circumscribed, flat-topped and hypopigmented papules--much like white seborrheic keratoses. Histologically however they merely show a thicker stratum corneum [CED 2013; 38:526].
No treatment is needed. Various interventions have been tried.
Tip cryotherapy (using a cotton-tipped applicator dipped in liquid nitrogen, not a spray gun) appears to be an effective therapy with minimal adverse effect for IGH [J Dermatolog Treat. 2016 Aug 23:1]. In that study, forty-three lesions were treated with cryotherapy and 58 lesions were assigned as control. 82.3% of the treated lesions comparing to only 2% of the control showed more than 75% improvement (p < .001).
Non-ablative fractional photothermal lysis laser showed some benefit [J Eur Dermatol Venereol 2014:Oct] as have some other lasers. Spot peeling with 80% phenol can induce some repigmentation [Indian Online Journal 2014:5:14]. Microneedle delivery of 5-FU was more effective than placebo in causing repigmentation [JAAD 2018;78;212]. The rationale here is that the 5-FU dissolves dermal fibrosis, allowing repigmentation to occur.
Multiple smaller lesions.
Indian Dermatol Online J 2015;6:164-7
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