A patient with melasma has tried topical hydroquinone 4% for 3 months with inadequate response. Histopathology of melasma skin shows increased melanin in both epidermis and dermis with occasional melanophages. This pattern is called:
- A Mixed type — intermediate treatment response; best identified by Wood's lamp examination ✓
- B Epidermal type — best response to treatment
- C Dermal type — best response to topical hydroquinone
- D Indeterminate type — seen in dark-skinned patients on Wood's lamp
Explanation
Melasma is classified histopathologically into epidermal (superficial, melanin in basal/suprabasal keratinocytes), dermal (melanin-laden melanophages in dermis), and mixed types. Clinically, Wood's lamp (365 nm UVA) helps classify: epidermal type shows enhanced contrast (accentuated pigment), dermal type shows no enhancement, and mixed type shows partial enhancement. Mixed type has intermediate treatment response. Dermal melasma responds least to topical agents including hydroquinone because the pigment is in the dermis beyond the reach of tyrosinase inhibitors. Indeterminate type is seen in Fitzpatrick skin types V-VI where Wood's lamp cannot differentiate epidermal from dermal pigment due to background melanin.
Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.