Differential Diagnosis for New Itchy Rash and Swelling
Single Most Likely Diagnosis
- Atopic Dermatitis (Eczema): Given the itchy nature of the rash and its location on the upper legs and chest, atopic dermatitis is a strong consideration. The absence of fever and the description of the rash suggest a dermatological rather than infectious etiology.
Other Likely Diagnoses
- Contact Dermatitis: This could be due to exposure to new soaps, detergents, or other allergens that come into contact with the skin, leading to an itchy rash. The distribution on the upper legs and chest could be consistent with exposure to certain products.
- Urticaria: Although typically more transient and migratory, urticaria (hives) can present with itchy lesions and could be considered, especially if the rash is more evanescent.
- Insect Bites: Could cause itchy lesions, especially if the patient has been outdoors or exposed to environments where insects are prevalent.
Do Not Miss Diagnoses
- Angioedema: Especially with the new swelling in the right jaw, angioedema must be considered. This condition can be life-threatening if it involves the airway, and its diagnosis is critical.
- Cellulitis or Abscess: Although less likely given the itchy nature and distribution of the rash, any skin infection could potentially lead to swelling and should be considered, especially if there's a history of trauma or infection.
- Lymphoma: Though rare, cutaneous T-cell lymphoma (like mycosis fungoides) can present with skin lesions and should be considered in the differential, especially with persistent or unusual rashes.
Rare Diagnoses
- Pityriasis Rosea: Characterized by a herald patch followed by a secondary eruption of oval-shaped lesions, typically on the trunk. It's less common but could fit the description if the rash has a distinctive morphology.
- Kawasaki Disease: Although typically seen in younger children, Kawasaki disease can present with rash, fever (which is not present here), and swelling, particularly of the hands and feet, but also potentially the face.
- Dermatomyositis: An autoimmune condition that can cause skin rash and muscle weakness. The rash often involves the face, chest, and extremities, and there could be swelling, particularly of the eyelids and hands.