Differential Diagnosis for Swelling and Itching of Right Hand and Foot

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 swelling, itching, and sometimes blistering. Given the localized nature of the symptoms to one hand and one foot, an external cause such as exposure to a new soap, detergent, or plant is plausible.

Other Likely Diagnoses

• Allergic Reaction: An allergic reaction to food, medication, or an insect bite could cause localized swelling and itching. The reaction could be part of a larger systemic response but is often confined to the area of contact.
• Insect Bite or Sting: Insect bites or stings can cause localized swelling, redness, and itching. The symptoms are usually self-limiting but can be severe in some cases.
• Cellulitis: A bacterial infection of the skin and subcutaneous tissues, cellulitis can cause swelling, redness, warmth, and sometimes itching. It typically starts as a small area of redness that spreads, and while it can occur anywhere, it often follows a break in the skin.

Do Not Miss Diagnoses

• Deep Vein Thrombosis (DVT): Although DVT typically presents with pain and swelling, it can occasionally cause itching due to inflammation of the vein. It's a critical diagnosis to consider because of the risk of pulmonary embolism.
• Erythema Multiforme: A skin condition characterized by target lesions, erythema multiforme can sometimes present with itching and swelling. It can be triggered by infections or medications and, in severe cases, can involve mucous membranes.
• Angioedema: Part of an allergic reaction, angioedema involves deeper layers of the skin and can cause significant swelling, sometimes with itching. It can be life-threatening if it involves the airways.

Rare Diagnoses

• Lymphoma: Certain types of lymphoma can cause skin symptoms, including itching and swelling, although this would typically be part of a more systemic illness.
• Sarcoidosis: A condition that can affect multiple parts of the body, sarcoidosis can cause skin lesions, swelling, and itching, among other symptoms.
• Erythromelalgia: A disorder that causes burning pain, heat, and redness in the hands and feet, erythromelalgia can sometimes present with swelling and itching, particularly in response to warmth or exertion.

Each of these diagnoses has a different set of implications for treatment and prognosis, highlighting the importance of a thorough diagnostic evaluation.