Differential Diagnosis for Semi-Annular Plaques on Lower Legs in a Child
Single Most Likely Diagnosis
- Tinea corporis (ringworm): This is a common fungal infection in children, characterized by annular or semi-annular plaques with a clear center, often found on the legs. The appearance and location of the lesions, along with the age of the patient, make this a highly probable diagnosis.
Other Likely Diagnoses
- Eczema (atopic dermatitis): While eczema can present with a variety of skin lesions, it can sometimes appear as semi-annular plaques, especially in the context of chronic scratching and skin thickening.
- Psoriasis: Although less common in children, psoriasis can manifest as annular or semi-annular plaques, particularly on the lower legs. The presence of other psoriatic lesions or a family history could support this diagnosis.
- Pityriasis rosea: This condition often starts with a herald patch followed by a secondary eruption of oval-shaped lesions, which can sometimes appear semi-annular, particularly on the trunk, but can also be found on the legs.
Do Not Miss Diagnoses
- Lyme disease (erythema migrans): Although typically presenting as a singular expanding lesion, in some cases, erythema migrans can appear as multiple semi-annular plaques. Given the potential serious consequences of untreated Lyme disease, it's crucial to consider this diagnosis, especially in endemic areas.
- Cutaneous leishmaniasis: This parasitic infection can cause skin lesions that might resemble semi-annular plaques, particularly if they are chronic and not responding to typical treatments. Travel history or exposure to endemic areas would increase the likelihood of this diagnosis.
Rare Diagnoses
- Granuloma annulare: A benign condition characterized by the presence of papular lesions arranged in an annular or semi-annular pattern, more commonly found on the hands and feet but can occur on the legs.
- Annular lichen planus: A variant of lichen planus that can present with annular or semi-annular lesions, which is less common in children but should be considered in the differential diagnosis due to its distinct clinical and histological features.
- Sarcoidosis: Although rare in children, cutaneous sarcoidosis can manifest with a variety of skin lesions, including annular or semi-annular plaques. Systemic symptoms or other organ involvement would support this diagnosis.