Differential Diagnosis for Red Splotchy Rash on Legs

Single Most Likely Diagnosis

• Cellulitis: This is a common bacterial skin infection that can cause redness, swelling, and warmth, often starting as a small area that spreads. The legs are a frequent site, and it can present with a splotchy appearance.

Other Likely Diagnoses

• Eczema (Dermatitis): Atopic dermatitis or contact dermatitis can cause red, itchy, and splotchy rashes on the legs, especially if there's exposure to allergens or irritants.
• Keratosis Pilaris: A harmless condition that causes small, rough, sandpaper-like bumps on the skin, often on the legs, which can appear red and splotchy.
• Folliculitis: An inflammation of the hair follicles, which can look like red, splotchy bumps, often due to bacterial or fungal infections.

Do Not Miss Diagnoses

• Deep Vein Thrombosis (DVT): While not typically thought of as a rash, DVT can cause redness and swelling of the leg, which might be mistaken for a splotchy rash. It's critical to consider this due to the risk of pulmonary embolism.
• Meningococcemia: A severe infection that can cause a rash, which might initially appear as red splotches. It's life-threatening and requires immediate medical attention.
• Rocky Mountain Spotted Fever (RMSF): A tick-borne illness that can cause a characteristic rash, often starting on the legs. It's critical to diagnose early due to the risk of severe complications.

Rare Diagnoses

• Erythema Nodosum: A condition characterized by the sudden formation of painful, red lumps on the skin, often on the legs. It can be associated with various underlying conditions, including infections and autoimmune diseases.
• Cutaneous Vasculitis: Inflammation of the blood vessels in the skin, which can cause a variety of rashes, including red, splotchy lesions on the legs. It can be associated with systemic diseases or medications.