Differential Diagnosis for Leg Swelling after a Bug or Mosquito Bite
- Single most likely diagnosis:
- Insect bite reaction (e.g., mosquito or bug bite): This is the most likely diagnosis given the history of a bug or mosquito bite at the weekend, followed by leg swelling. Most insect bites cause a localized reaction that can include swelling, redness, and itching.
- Other Likely diagnoses:
- Cellulitis: A bacterial infection of the skin and subcutaneous tissues that can occur after an insect bite, especially if the bite becomes infected. Symptoms include redness, swelling, warmth, and tenderness of the skin.
- Contact dermatitis: An allergic reaction to substances like insect repellents or other topical treatments applied after the bite, leading to skin inflammation and swelling.
- Urticaria: Hives can cause swelling and are often triggered by allergic reactions, which could be related to the insect bite.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
- Necrotizing fasciitis: A severe bacterial infection that destroys tissue under the skin, including fat and the tissue covering the muscles (fascia). It's a medical emergency and can start with symptoms similar to cellulitis but progresses rapidly.
- Deep vein thrombosis (DVT): Although less directly related to the insect bite, any condition causing leg swelling should prompt consideration of DVT, especially if there are risk factors such as recent travel or immobility.
- Rare diagnoses:
- Lymphangitis: An infection of the lymphatic vessels, which can cause red streaks and swelling, typically following a bite or wound.
- Erythema migrans (Lyme disease): If the bite was from a tick, there's a possibility of Lyme disease, characterized by a distinctive expanding rash (erythema migrans) at the site of the bite, though this is more common in specific geographic areas.
- Anaphylaxis: A severe, life-threatening allergic reaction that can occur within minutes of an insect bite, though it would typically present with more systemic symptoms such as difficulty breathing, rapid heartbeat, and a fall in blood pressure, in addition to swelling.