Differential Diagnosis for a Single Scaly Well-Defined Rash on the Forehead
Single Most Likely Diagnosis
- Seborrheic Keratosis: A common, benign skin growth that can appear as a single, well-defined, scaly rash, often on the face, including the forehead. Its appearance and the patient's age make it a likely candidate.
Other Likely Diagnoses
- Actinic Keratosis: A small, rough, scaly patch on the skin that develops from years of exposure to the sun, which could explain a single lesion on the forehead. It's more common in older adults but can occur in younger individuals with significant sun exposure.
- Eczema (Nummular Dermatitis): Characterized by coin-shaped patches of dry, scaly skin, which could present as a single lesion on the forehead, especially if the patient has a history of atopic diseases.
- Psoriasis: While typically presenting with multiple lesions, psoriasis can occasionally start with a single plaque, especially on the scalp or face, including the forehead.
Do Not Miss Diagnoses
- Basal Cell Carcinoma: The most common form of skin cancer, which can present as a single, well-defined lesion that may be scaly. Early detection is crucial for effective treatment.
- Squamous Cell Carcinoma: Another form of skin cancer that can appear as a firm, rough, scaly lesion, often on sun-exposed areas like the forehead.
- Malignant Melanoma: Although less likely given the description of a scaly, well-defined rash, any new or changing skin lesion warrants consideration of melanoma due to its potential severity.
Rare Diagnoses
- Discoid Lupus Erythematosus: An autoimmune disease that can cause scaly, disk-shaped lesions on the face, including the forehead, but it's less common and typically presents with more systemic symptoms or multiple lesions.
- Granuloma Faciale: A rare skin condition characterized by single or multiple, well-defined, reddish-brown plaques, typically on the face, which could be considered if other diagnoses are ruled out.
- Lichen Planus: An inflammatory condition that can affect the skin, presenting with purplish, itchy, flat bumps, but it's less likely given the single lesion description and the typical presence of mucosal involvement or multiple lesions.