Chronic Venous Insufficiency: This condition is characterized by the veins having problems returning blood from the legs back to the heart due to valve issues, leading to fluid accumulation and pitting edema. It's a common cause of lower extremity edema, especially in individuals with a history of deep vein thrombosis, obesity, or those who stand for long periods.

Heart Failure: Reduced cardiac output can lead to fluid buildup in the body, often manifesting as pitting edema in the lower extremities. Patients might also exhibit shortness of breath, fatigue, and other signs of heart failure.
Nephrotic Syndrome: A collection of symptoms indicating severe damage to the kidneys' filtration system, leading to significant protein loss in the urine. This loss can cause hypoalbuminemia, which decreases the oncotic pressure in blood vessels, resulting in fluid leakage into the interstitial space and edema.
Liver Cirrhosis: Cirrhosis can lead to hypoalbuminemia and also cause portal hypertension, which can lead to fluid accumulation in the form of ascites and peripheral edema.
Deep Vein Thrombosis (DVT): Although DVT typically causes non-pitting edema, in some cases, especially if there's significant inflammation, it might present with pitting edema. It's essential to consider DVT due to its potential for serious complications like pulmonary embolism.

Pulmonary Embolism: While not directly causing pitting edema, pulmonary embolism can lead to right heart strain, which might result in peripheral edema. It's crucial to consider this diagnosis due to its high mortality rate if untreated.
Superior Vena Cava Syndrome: Obstruction of the superior vena cava can lead to edema of the upper body but, in some cases, might also affect the lower extremities if there's significant collateral circulation involvement.
Lymphoma or Other Malignancies: Certain cancers can cause edema through various mechanisms, including obstruction of lymphatic or venous return. Although less common, these diagnoses are critical not to miss due to their significant implications for patient management and prognosis.

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 simple obesity but doesn't typically reduce with weight loss.
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 including the skin, kidneys, heart, and nervous system. Edema can be a part of its presentation.
Sarcoidosis: An inflammatory disease that affects multiple organs in the body, which can lead to edema among other symptoms, though it's a less common cause of pitting edema in the lower extremities.