Differential Diagnosis for Bilateral Swelling with a Small Scab Over a Dime-Sized Lesion

Single Most Likely Diagnosis

• Cellulitis or Skin Infection: This is a common condition that can cause bilateral swelling, especially if the infection is severe or spreading. The presence of a small scab over a dime-sized lesion could indicate a localized infection or the site of infection entry.

Other Likely Diagnoses

• Insect Bites or Stings: Multiple bites or stings can cause bilateral swelling, and a small scab could form over the bite or sting site as it heals.
• Allergic Contact Dermatitis: An allergic reaction to something that has come into contact with the skin could cause swelling and lesions, potentially with scabbing as the skin reacts and then starts to heal.
• Eczema (Atopic Dermatitis): This condition can cause skin inflammation, leading to swelling and lesions that might scab over, especially if scratched.

Do Not Miss Diagnoses

• Necrotizing Fasciitis: Although rare, this is a life-threatening condition that requires immediate medical attention. It can start with symptoms similar to cellulitis but progresses rapidly, causing severe pain, swelling, and potentially skin necrosis.
• Methicillin-Resistant Staphylococcus aureus (MRSA) Infection: MRSA can cause skin infections that might appear as swollen, painful lesions that scab over. It's crucial to identify and treat MRSA infections promptly due to their resistance to many antibiotics.
• Lymphoma or Other Malignancies: In rare cases, skin lesions and swelling could be indicative of an underlying malignancy, such as lymphoma. Although less likely, missing such a diagnosis could have severe consequences.

Rare Diagnoses

• Erythema Multiforme: A skin condition characterized by target lesions, which could potentially scab over. It's often triggered by infections or medications.
• Sweet Syndrome (Acute Febrile Neutrophilic Dermatosis): Characterized by fever, neutrophilia, and tender, erythematous skin lesions that can sometimes resemble scabs or ulcers.
• Pyoderma Gangrenosum: A rare condition that causes painful ulcers, which might initially appear as small, scabbed lesions and can be associated with systemic diseases.

Each of these diagnoses has different implications for treatment and patient outcomes, emphasizing the importance of a thorough evaluation to determine the underlying cause of the symptoms.