Differential Diagnosis for Widespread Annular Patches and Papules
Single Most Likely Diagnosis
- Tinea corporis (ringworm): This condition is characterized by annular patches and papules with scale, often starting as a single lesion that spreads to other areas of the body. The description of an oval-shaped patch starting behind the knee and then spreading to the trunk, back, arms, and behind the ear is consistent with the typical presentation of tinea corporis.
Other Likely Diagnoses
- Pityriasis rosea: This condition often starts with a herald patch, followed by a widespread eruption of oval-shaped patches with scale, typically on the trunk and proximal extremities. The timing and description of the lesions are consistent with pityriasis rosea.
- Eczema (nummular dermatitis): This condition can present with annular patches and papules, often with scale, and can be widespread. However, the absence of a clear history of atopy or skin barrier disruption makes this diagnosis less likely.
- Psoriasis: While psoriasis can present with annular plaques, the presence of scale and the distribution of lesions are not as typical for this condition.
Do Not Miss Diagnoses
- Lyme disease (erythema migrans): This condition can present with an expanding annular patch, often with central clearing, and can be accompanied by systemic symptoms. Given the potential for serious complications if left untreated, Lyme disease should be considered in the differential diagnosis, especially if the patient has a history of tick exposure.
- Syphilis (secondary syphilis): This condition can present with a wide range of skin manifestations, including annular patches and papules. The presence of systemic symptoms, such as fever or lymphadenopathy, would increase the suspicion for syphilis.
Rare Diagnoses
- Granuloma annulare: This condition is characterized by annular patches with papules, often on the extremities. While it can be widespread, it is less common than other conditions on this list.
- Sarcoidosis: This condition can present with skin lesions, including annular patches and papules, but is often accompanied by systemic symptoms, such as lung or eye involvement. The absence of these symptoms makes this diagnosis less likely.