Differential Diagnosis for 11 y/o with Sandpaper-like Rash 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 the description of the rash as feeling like sandpaper make this a highly plausible diagnosis.
• Other Likely diagnoses:
  • Eczema (Atopic Dermatitis): This is a chronic skin condition that can cause dry, itchy, and rough skin, which might feel like sandpaper. It often affects the arms and is common in children.
  • Dry Skin (Xerosis): Especially during dry weather or with excessive washing, the skin on the arms can become very dry and rough, feeling similar to sandpaper.
• Do Not Miss diagnoses:
  • Scabies: Although less likely, scabies can cause a severe itch and a rash that might feel rough. It's contagious and requires prompt treatment to prevent spread.
  • Allergic Contact Dermatitis: This is a skin reaction that occurs after contact with an allergen or irritant. It can cause a rash that might feel rough and is important to diagnose to avoid further exposure to the causative agent.
• Rare diagnoses:
  • Ichthyosis: A group of skin conditions that cause dry, scaly, or thick skin, which could potentially feel like sandpaper. These conditions are less common and often have a genetic component.
  • Phrynoderma (Toad Skin): A rare condition characterized by a rough, dry, sandpaper-like skin texture, often associated with nutritional deficiencies or environmental factors. It's less common but should be considered if other diagnoses are ruled out.