Chronic Venous Insufficiency: This condition is a common cause of bilateral lower extremity edema, especially in older adults or those with a history of deep vein thrombosis. It occurs due to the incompetence of venous valves, leading to blood pooling in the legs.

Heart Failure: Bilateral edema can be a sign of fluid overload in heart failure, particularly right-sided heart failure. It results from the heart's inability to pump blood effectively, leading to fluid accumulation in the peripheral tissues.
Nephrotic Syndrome: This condition involves significant proteinuria, leading to hypoalbuminemia, which can cause fluid to shift from the vascular space to the interstitial space, resulting in edema.
Liver Cirrhosis: Cirrhosis can lead to fluid retention and edema due to hypoalbuminemia and portal hypertension.
Hypothyroidism: Although less common, 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, as it can be life-threatening if it leads to pulmonary embolism. Bilateral DVT, though less common, can occur and must be considered.
Lymphoma or Other Malignancies: Certain cancers can cause lymphatic obstruction or increased vascular permeability, leading to edema. Early detection is critical for treatment and prognosis.
Superior Vena Cava Syndrome: Obstruction of the superior vena cava can lead to edema of the upper body but can also affect the lower extremities if the obstruction is significant and affects venous return.

Lipedema: A chronic condition characterized by the abnormal growth of fat cells in the legs, leading to swelling and pain. It's often mistaken for lymphedema or obesity.
Fabry Disease: A genetic disorder that leads to the accumulation of a particular type of fat in the body's cells, affecting many parts of the body and potentially causing edema among other symptoms.
Milroy Disease: A rare, inherited condition characterized by chronic lymphedema, typically presenting in one leg but can be bilateral.