The causes of nephrotic syndrome can be broadly classified into primary and secondary causes:
### Primary Causes
Primary nephrotic syndrome originates in the kidneys and includes:
1. **Minimal Change Disease (MCD)**:
- The most common cause in children.
- Characterized by damage to the podocytes (cells in the kidneys that filter blood).
- Often idiopathic but can be associated with infections, allergic reactions, and certain medications.
2. **Focal Segmental Glomerulosclerosis (FSGS)**:
- Scarring in scattered regions of the kidneys.
- Can be idiopathic or secondary to other conditions like obesity, infections, or drug use.
3. **Membranous Nephropathy (MN)**:
- Thickening of the glomerular basement membrane.
- Often idiopathic but can be associated with autoimmune diseases, infections, or malignancies.
### Secondary Causes
Secondary nephrotic syndrome is due to systemic diseases or conditions affecting the kidneys, including:
1. **Diabetes Mellitus**:
- Diabetic nephropathy is a leading cause of nephrotic syndrome in adults.
- Damage to the kidney’s filtering system due to chronic high blood sugar levels.
2. **Lupus Nephritis**:
- A complication of systemic lupus erythematosus (SLE), an autoimmune disease.
- Inflammation and damage to kidney tissues.
3. **Amyloidosis**:
- Deposition of abnormal protein (amyloid) in kidney tissues.
- Can be associated with multiple myeloma or chronic inflammatory diseases.
4. **Infections**:
- Hepatitis B and C, HIV, malaria, and certain bacterial infections can lead to nephrotic syndrome.
5. **Drugs and Toxins**:
- NSAIDs, certain antibiotics, gold salts, penicillamine, and heroin can cause nephrotic syndrome.
6. **Malignancies**:
- Cancers like lymphoma and leukemia can be associated with nephrotic syndrome.
### Genetic Causes
Certain inherited conditions can also lead to nephrotic syndrome, such as:
1. **Congenital Nephrotic Syndrome**:
- Caused by genetic mutations affecting kidney function, evident at birth or in early childhood.
### Mechanisms and Pathophysiology
The underlying mechanism often involves damage to the glomeruli, the tiny filtering units within the kidneys. This damage leads to increased permeability, allowing proteins, especially albumin, to leak into the urine. The resulting protein loss from the blood leads to hypoalbuminemia, reducing oncotic pressure and causing edema. The liver compensates by producing more lipids, resulting in hyperlipidemia.
### Conclusion
Nephrotic syndrome can arise from a variety of primary kidney diseases or as a consequence of systemic conditions. Diagnosis typically involves urine and blood tests, and sometimes kidney biopsy, to determine the underlying cause and guide treatment. Treatment strategies vary depending on the cause but often include managing symptoms and addressing the underlying disease.