Differential Diagnosis for Multiple Well-Defined Erythematous and Hyperpigmented Round Papules
Single Most Likely Diagnosis
- Lichen planus: This condition is characterized by the presence of well-defined, erythematous, and hyperpigmented papules, often localized on the extremities, including the arms. The bilateral and symmetric distribution of the lesions supports this diagnosis.
Other Likely Diagnoses
- Keratosis pilaris: This is a common skin condition that presents with multiple small, round, erythematous papules, often on the arms. While it typically has a more follicular distribution, it could be considered in the differential.
- Pityriasis rosea: Although it often starts with a herald patch, pityriasis rosea can present with multiple oval-shaped erythematous patches, which might be considered in the differential, especially if the patient reports a recent onset.
- Nummular dermatitis: This condition presents with well-defined, coin-shaped patches of dermatitis, which can be erythematous and hyperpigmented. It often occurs on the arms and legs.
Do Not Miss Diagnoses
- Sarcoidosis: While less common, sarcoidosis can present with skin lesions that are erythematous and hyperpigmented. Given its potential for systemic involvement, including pulmonary and ocular manifestations, it is crucial not to miss this diagnosis.
- Lupus erythematosus: Systemic lupus erythematosus (SLE) can present with a variety of skin manifestations, including erythematous and hyperpigmented papules. The potential for systemic involvement makes this a critical diagnosis not to overlook.
Rare Diagnoses
- Erythema elevatum diutinum: A rare skin condition characterized by red, purple, or brown lesions that are typically found on the extensor surfaces of the arms and legs. It is associated with various systemic diseases, including infections and hematologic disorders.
- Granuloma annulare: This condition can present with papular lesions that are erythematous and can become hyperpigmented over time. While it is more common in children and often localized to the hands and feet, it could be considered in adults with atypical presentations.