Differential Diagnosis for Non-Blanching Rash on Edematous Lower Legs Bilaterally

Single Most Likely Diagnosis

• Chronic Venous Insufficiency (CVI): This condition is characterized by the inability of veins to return blood to the heart due to valve issues, leading to edema, skin changes, and potentially a non-blanching rash. The edematous lower legs bilaterally with a non-blanching rash are classic signs of advanced CVI.

Other Likely Diagnoses

• Cellulitis: An infection of the skin and subcutaneous tissues, which can cause redness, swelling, warmth, and a non-blanching rash. The presence of edema and a rash on the lower legs could suggest cellulitis, especially if there's a history of trauma or infection.
• Deep Vein Thrombosis (DVT): While DVT typically presents with unilateral symptoms, it can occasionally present bilaterally. The edema and potential for a non-blanching rash due to inflammation and possible skin necrosis make DVT a consideration.
• Lymphedema: Chronic swelling due to lymphatic system dysfunction can lead to skin changes, including a non-blanching rash. The bilateral edema could suggest a systemic or genetic cause of lymphedema.

Do Not Miss Diagnoses

• Necrotizing Fasciitis: A severe infection that destroys tissue under the skin, including fat and the tissue covering the muscles (fascia). It's a medical emergency that can present with a non-blanching rash, edema, and severe pain. Early diagnosis is crucial for survival.
• Warfarin-Induced Skin Necrosis: A rare but potentially deadly condition associated with warfarin therapy, especially in the first few days of treatment. It presents with skin necrosis, often on areas with more fatty tissue like the breasts, thighs, and buttocks, but can occur on the legs.
• Purpura Fulminans: A rare, life-threatening condition characterized by rapid progression of hemorrhagic necrosis of the skin, often associated with severe infections or genetic disorders. It presents with a non-blanching rash that can resemble bruises.

Rare Diagnoses

• Erythema Elevatum Diutinum (EED): A rare skin condition characterized by red, purple, or brown lesions that typically occur on the extensor surfaces of the extremities. It can be associated with various systemic diseases, including infections and autoimmune disorders.
• Malignant Panniculitis: A rare condition where there's inflammation of the subcutaneous fat, which can be associated with underlying malignancies. It presents with skin lesions, including a non-blanching rash, and edema.