Differential Diagnosis for Forearm Rash
Single Most Likely Diagnosis
- Contact Dermatitis: This is a common condition that occurs when the skin comes into contact with an irritant or allergen, leading to a rash. The forearm is a common site for contact dermatitis due to exposure to various substances such as soap, detergent, or plants.
Other Likely Diagnoses
- Eczema (Atopic Dermatitis): A chronic skin condition characterized by itchy, inflamed skin. The forearm can be one of the areas affected, especially if the individual has a history of atopic diseases.
- Psoriasis: An autoimmune condition that speeds up the life cycle of skin cells, causing cells to build up rapidly on the surface of the skin. The forearms can be a common site for psoriatic plaques.
- Insect Bites: Mosquitoes, bed bugs, and other insects can cause rashes on the forearm, especially during outdoor activities or in infested environments.
Do Not Miss Diagnoses
- Lyme Disease: Caused by the bacterium Borrelia burgdorferi, transmitted to humans through the bite of infected black-legged ticks. The initial sign is often a distinctive rash (erythema migrans) that can appear on various parts of the body, including the forearm.
- Cellulitis: A bacterial skin infection that can cause redness, swelling, and warmth of the skin. It requires prompt antibiotic treatment to prevent serious complications.
- Allergic Reaction to Medication: Certain medications can cause skin rashes as part of an allergic reaction. Identifying and stopping the offending drug is crucial.
Rare Diagnoses
- Pityriasis Rosea: A rare skin condition characterized by a rash that typically starts with a single, large spot (herald patch) followed by an eruption of smaller spots, which can appear on the forearms among other areas.
- Dermatomyositis: A type of inflammatory myopathy characterized by skin rash and muscle weakness. The rash can appear on various parts of the body, including the forearms, and is often accompanied by other systemic symptoms.
- Leprosy (Hansen's Disease): A chronic bacterial infection that primarily affects the skin, nerves, and mucous membranes. It can cause skin lesions, including rashes, which can appear on the forearms, though it is relatively rare in many parts of the world.