Heart Failure: This is often the most common cause of bilateral pitting edema due to the inability of the heart to pump blood effectively, leading to fluid buildup in the body, particularly in the legs.

Nephrotic Syndrome: Characterized by significant proteinuria, hypoalbuminemia, and edema, nephrotic syndrome is a common cause of bilateral pitting edema due to the loss of albumin, which leads to decreased oncotic pressure and fluid leakage into the interstitial space.
Liver Cirrhosis: Cirrhosis can lead to hypoalbuminemia and portal hypertension, both of which contribute to the development of edema.
Chronic Venous Insufficiency: This condition leads to increased pressure in the veins of the legs, causing fluid to leak into the surrounding tissue and resulting in edema.
Hypothyroidism: Can cause edema due to the accumulation of mucopolysaccharides in the skin and other tissues.

Deep Vein Thrombosis (DVT): Although DVT typically presents unilaterally, it's crucial not to miss it, especially if there's a suspicion of pulmonary embolism, which can be life-threatening.
Lymphoma or Other Malignancies: Certain cancers can cause edema, either directly by obstructing lymphatic or venous return or indirectly through the production of cytokines and other factors that lead to fluid retention.
Superior Vena Cava Syndrome: Obstruction of the superior vena cava can lead to edema of the upper body, which, while less common, is critical to diagnose due to its potential for serious complications.

Lipedema: A chronic condition characterized by the abnormal growth of fat cells in the legs, leading to swelling and edema.
Myxedema: A condition associated with hypothyroidism, characterized by the deposition of mucin in the skin and other tissues, leading to non-pitting edema, but can sometimes present with pitting edema.
Fabry Disease: A rare genetic disorder that can lead to edema among other systemic symptoms due to the accumulation of globotriaosylceramide in various cells.
Sarcoidosis: A systemic disease that can cause edema through various mechanisms, including lymphatic obstruction and inflammation.