Stasis Dermatitis: This condition is characterized by skin inflammation and irritation due to fluid buildup (edema) in the legs, often associated with venous insufficiency. The symptoms of redness, swelling, and dermatitis on the leg align closely with stasis dermatatitis, especially considering the possible arterial issues which might indirectly contribute to poor circulation and exacerbate venous insufficiency.

Cellulitis: A bacterial skin infection that can cause redness, swelling, and warmth, often affecting the legs. Given the symptoms of redness and swelling, cellulitis is a plausible diagnosis, especially if there's a break in the skin that could serve as an entry point for bacteria.
Eczema (Atopic Dermatitis): While more common in children, eczema can occur at any age and may present with red, itchy, and swollen skin. If the dermatitis is not solely due to circulatory issues, eczema could be a consideration, especially if there's a personal or family history of atopy.
Contact Dermatitis: An allergic reaction or irritation caused by substances coming into contact with the skin. This could be a possibility if the patient has recently started using new soaps, creams, or has been exposed to allergens or irritants.

Deep Vein Thrombosis (DVT): Although DVT typically presents with pain and swelling, it's crucial not to miss this diagnosis due to the risk of pulmonary embolism. The presence of swelling and possible arterial issues makes it essential to consider DVT, especially if there are risk factors such as recent immobility, surgery, or cancer.
Arterial Occlusion: Given the mention of possible arterial issues, an acute arterial occlusion could present with similar symptoms, including pain, pallor, pulselessness, poikilothermia, paresthesias, and paralysis. This is a medical emergency requiring prompt intervention.
Necrotizing Fasciitis: A severe infection that destroys tissue under the skin, including fat and the tissue covering the muscles (fascia). It's a rare but life-threatening condition that requires immediate medical attention. Symptoms can include severe pain, swelling, and redness.

Lymphedema: A condition characterized by swelling in one or more extremities, resulting from impaired flow in the lymphatic vessels or lymph nodes. While it could explain swelling, it's less likely to cause acute redness and dermatitis unless there's an associated infection.
Erythema Nodosum: A type of skin inflammation that is located in a certain portion of the fatty layer of skin. It results in tender red nodules or patches, most commonly on the shins. It could be considered if the dermatitis presents with nodular characteristics and is accompanied by systemic symptoms.