Differential Diagnosis for a Small White Round Area with Balding on the Right Forehead

Physical Exam:

• Location: Right forehead, on the hairline
• Description: Small, white, round area with associated balding of the hair
• Size and Shape: To be determined on examination
• Margins: To be assessed for clarity and definition
• Surrounding Skin: To be evaluated for any signs of inflammation, erythema, or other lesions
• Hair Loss Pattern: Assess if the hair loss is localized to the described area or if there's a more widespread pattern

Differential Diagnoses:

• Single Most Likely Diagnosis:
  • Alopecia Areata: An autoimmune condition leading to patchy hair loss, often presenting with one or more round, smooth bald patches on the scalp. The presence of a small, white, round area with balding is highly suggestive of this condition.
• Other Likely Diagnoses:
  • Tinea Capitis (Ringworm of the Scalp): A fungal infection that can cause hair loss, often accompanied by a round, scaly, and sometimes red patch. The white appearance could be due to scaling.
  • Pityriasis Amiantacea: A condition characterized by the formation of yellowish, oily scales that mat the hair together, potentially leading to hair loss. It might appear white due to the scaling.
• Do Not Miss Diagnoses:
  • Basal Cell Carcinoma or Other Skin Cancers: Although less likely, skin cancers can present in unusual ways, including areas of hair loss. It's crucial to not miss these diagnoses due to their potential for serious consequences if left untreated.
  • Sarcoidosis: A condition that can cause skin lesions and hair loss, among other systemic symptoms. It's essential to consider due to its potential for multi-organ involvement.
• Rare Diagnoses:
  • Discoid Lupus Erythematosus: An autoimmune condition that can cause skin lesions and scarring hair loss. It's less common but should be considered, especially if there are other systemic symptoms.
  • Trichotillomania: A psychological condition leading to compulsive hair pulling, resulting in hair loss. The presentation might not typically include a white, round area, but it's a consideration in the differential diagnosis of hair loss.

Each diagnosis is justified based on the combination of hair loss and the specific characteristics of the lesion described. The single most likely diagnosis, Alopecia Areata, is chosen due to its common presentation with round, smooth bald patches. Other diagnoses are included based on their potential to cause similar symptoms, with an emphasis on not missing serious conditions like skin cancers. Rare diagnoses, though less likely, are important to consider for comprehensive evaluation.