Special Stains Used in Vitiligo
Useful special stains which can detect both active and dormant melanocytes include HMB45, Mel-5, and NKI/beteb. DOPA detects active melanocytes, and a pan-melanoma cocktail HMB45+tyrosinase+MART-1 (Melan-A) can maximize yield [13-15].
For research purposes, T-cell CD markers CD3 and CD8 are used to highlight and quantify infiltrating and dermal lymphocytes. CD 207/Langerin, integrin CD 11c, HLA-DR, DC-LAMP, and CD83 are additional immunohistochemical stains used to quantify and detect the activity of Langerhans and dermal dendritic cells.
Idiopathic Guttate Hypomelanosis (IGH)
IGH is characterized by 2-5 mm hypopigmented or porcelain-white macules usually seen on sun-exposed extremities of the elderly (Fig. 23.6a). Histopathologically, IGH is characterized by hyperkeratosis of the stratum corneum, atrophic epidermis with flattened rete ridges, decreased melanin content, and reduced melanocytes in the basal layer (Fig. 23.6b). In a study by Kim et al.  comparing lesional and normal skin, hyperkeratosis was a common feature in patients with IGH, but atrophic epidermis and flattened rete ridges were not. There was also a significantly decreased amount of melanin pigment and detectable melanocytes in the epidermal layers of IGH skin compared to normal skin. The decrease in pigmentation in IGH therefore could be due to decreased number and dysfunction of degenerative melanocytes in addition to a decreased number of melanosomes in some melanocytes.
IGH is thus characterized histopathologically by hyperkeratosis, decreased melanin, and melanocytes, in contrast to vitiligo where a complete loss of melanin pigment and absence of melanocytes are seen .
Fig. 23.6 (a) Clinical picture of idiopathic guttate hypomelanosis in brown skin and (b) histo- pathological findings of flattened rete ridges and markedly decreased number of melanocytes and melanin in the basal cell layer (H & E x100)
Fig. 23.7 (a) Pityriasis alba in a Filipino boy presenting as a hypopigmented patch on the cheeks and (b) histopathological findings of spongiosis and normal number of melanocytes in the basal cell layer (H & E x400)