Differential Diagnosis for an 11-Year-Old Boy with a Brown Ring Behind the Left Ear
Single Most Likely Diagnosis
- Mongolian spot: A benign flat congenital melanocytic lesion that can appear as a blue or brown mark, commonly found at the base of the spine or on the buttocks but can also occur in other areas, including behind the ear. It often fades by the age of 5 but can persist in some cases.
Other Likely Diagnoses
- Café-au-lait macule: A benign pigmented lesion that can appear anywhere on the body, including behind the ear. These lesions are usually light brown to dark brown and can be solitary or multiple.
- Nevus of Ito or Nevus of Ota: These are benign melanocytic lesions that can cause hyperpigmentation, typically around the eye (Nevus of Ota) or on the shoulder and supraclavicular area (Nevus of Ito). While less common, they could potentially present behind the ear.
- Dermal melanocytosis: A condition where melanocytes are present in the dermis, leading to blue or brown pigmentation. It's less common but could be considered given the description.
Do Not Miss Diagnoses
- Malignant melanoma: Although extremely rare in children, any pigmented lesion that is new, changing, or has characteristics concerning for malignancy (asymmetry, irregular borders, color variation, diameter >6mm, evolving) should be evaluated for melanoma.
- Neurofibromatosis type 1 (NF1): Café-au-lait spots are a hallmark of NF1, and while the presence of a single brown ring might not be diagnostic, it's essential to consider NF1, especially if other signs such as neurofibromas, axillary or inguinal freckling, or Lisch nodules are present.
Rare Diagnoses
- Ephelides (freckles): While common, the description of a "brown ring" is less typical for freckles, which are usually smaller and more numerous.
- Congenital melanocytic nevus: These can appear anywhere on the body and have a varied appearance. They are generally present at birth or appear shortly after.
- Incontinentia pigmenti: A rare genetic disorder that affects the skin, hair, teeth, and central nervous system. Skin lesions evolve through several stages, including blistering, verrucous, hyperpigmented, and atrophic phases. The hyperpigmented stage could potentially be mistaken for a brown ring.