Differential Diagnosis for 11 y/o with Small Round Papules on Bilateral Arms

• Single Most Likely Diagnosis
  • Keratosis Pilaris: This condition is characterized by small, rough, sandpaper-like bumps on the skin, often on the arms, and is very common in children and adolescents. The bilateral distribution and description of small round papules make it a strong candidate.
• Other Likely Diagnoses
  • Eczema (Atopic Dermatitis): Can present with papules, especially if the skin is scratched, leading to lichenification. The bilateral arm involvement could be consistent with this, especially if there's a history of atopy.
  • Folliculitis: An inflammation of the hair follicles, which can appear as small papules or pustules, often due to bacterial or fungal infections. This could be a consideration, especially if there's a history of shaving, tight clothing, or excessive sweating.
  • Pityriasis Alba: A mild form of eczema that presents as small, round, faint patches on the skin, often on the face but can appear on arms. It's common in children and could fit the description given.
• Do Not Miss Diagnoses
  • Sarcoidosis: Although rare in children, sarcoidosis can present with skin lesions, including papules. It's a systemic disease that can affect multiple organs, making early diagnosis crucial.
  • Lymphoma (Cutaneous T-Cell Lymphoma): Certain types of lymphoma can initially present with skin lesions that might resemble benign conditions. Early recognition is vital due to the potential severity of the disease.
• Rare Diagnoses
  • Tuberous Sclerosis: A genetic disorder that can cause skin lesions, including angiofibromas (previously known as adenoma sebaceum), which might appear as small papules. The condition is rare and usually associated with other systemic findings.
  • Neurofibromatosis: Characterized by neurofibromas, cafe-au-lait spots, and other skin findings. While the primary lesions might not exactly match the description, the condition's rarity and potential for other associated findings make it worth mentioning in a broad differential diagnosis.