Idiopathic Edema: This condition is characterized by swelling in the legs and arms without an identifiable cause, often seen in individuals with no underlying medical conditions. It's a common diagnosis when other causes are ruled out.

Venous Insufficiency: Problems with the veins returning blood from the legs to the heart can lead to fluid accumulation, causing oedema. This is a common issue, especially in individuals who stand for long periods.
Lymphatic Obstruction: Any blockage in the lymphatic system can prevent proper fluid drainage, leading to oedema. This could be due to various reasons, including previous surgeries or infections.
Medication Side Effects: Certain medications, such as calcium channel blockers, can cause oedema as a side effect. Even though the patient has no comorbidities, it's essential to consider any over-the-counter or prescribed medications.
Sodium Retention: Excessive sodium intake can lead to fluid retention, causing oedema. This is particularly relevant in individuals with high sodium diets.

Deep Vein Thrombosis (DVT): Although less likely without other symptoms, DVT is a potentially life-threatening condition that must be considered. It involves a blood clot in the deep veins, usually in the legs, which can cause oedema.
Nephrotic Syndrome: Despite normal kidney function tests, nephrotic syndrome (characterized by significant proteinuria, hypoalbuminemia, and oedema) can sometimes present with relatively preserved renal function. It's crucial to check for proteinuria.
Hypothyroidism: This condition can cause oedema and might not be immediately suspected without specific symptoms like fatigue or weight gain. However, it's a critical diagnosis not to miss due to its implications on overall health.

Lipedema: A chronic condition characterized by the abnormal growth of fat cells in the legs, leading to swelling. It's more common in women but can occur in men.
Fabry Disease: A rare genetic disorder that can cause oedema among other symptoms, due to the accumulation of a particular type of fat in the body's cells.
Sarcoidosis: An autoimmune disease that can affect various parts of the body, including the lymph nodes, and potentially cause oedema. It's rare but should be considered in the differential diagnosis due to its varied presentations.