Differential Diagnosis for Discolouration of the Centre of the Forehead and Above the Eyebrows

• Single most likely diagnosis
  • Melasma: This condition is characterized by patches of discoloration, typically on the face, and is often described as having a "tanned" appearance. It is more common in individuals with higher melanin levels and can be exacerbated by sun exposure, hormonal changes, and certain medications.
• Other Likely diagnoses
  • Post-inflammatory hyperpigmentation (PIH): Although the question states that the area is not itchy, red, dry, or scaly, PIH could still be a consideration if there was a previous inflammatory event that has since resolved. PIH can result in hyperpigmented areas that resemble a tan.
  • Berloque dermatitis: This is a condition caused by the use of certain fragrances or perfumes that contain bergamot oil, leading to phototoxic reactions and subsequent hyperpigmentation upon sun exposure. The pattern of discoloration could potentially match the described area.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Addison's disease: Although rare, Addison's disease (primary adrenal insufficiency) can cause hyperpigmentation, particularly in areas exposed to the sun, as well as in palmar creases, scars, and mucous membranes. The hyperpigmentation is due to increased levels of adrenocorticotropic hormone (ACTH), which stimulates melanin production.
• Rare diagnoses
  • Erythema ab igne: This condition is caused by prolonged exposure to heat (such as from a heating pad or laptop) and can result in reticulated hyperpigmentation. While it typically occurs on the legs or lap area, it could potentially occur on the face if there is a habit of applying heat in that area.
  • Carotenemia: This is a harmless condition caused by excessive consumption of carotenoid-rich foods (like carrots), leading to a yellow-orange discoloration of the skin. However, it would not typically be localized to the forehead and eyebrows.