Causes of Secondary Membranous Nephropathy in Adults
Secondary membranous nephropathy in adults is caused by systemic autoimmune diseases, infections, drugs, and malignancies, accounting for approximately 20-30% of all MN cases 1, 2, 3.
Major Categories of Secondary Causes
Systemic Autoimmune Diseases
- Systemic lupus erythematosus (SLE) - the most common autoimmune cause, presenting as Class V lupus nephropathy 1, 4, 3
- Other autoimmune conditions 5, 4
Infections
- Hepatitis B virus - a well-established infectious cause 1, 2, 4
- Hepatitis C virus 3
- Other viral infections 3
Medications and Drugs
- Drug-induced MN is a recognized secondary cause 1, 2, 4, 3
- Specific causative agents vary but should be systematically reviewed in any patient presenting with MN
Malignancies
- Solid tumors and hematologic malignancies are important causes of secondary MN 1, 2, 4, 3
- Recent evidence identifies specific antigens like THSD7A and NELL-1 that may be associated with malignancy-related MN 6
- The association between certain MN-specific antigens and malignant tumors is an area of active investigation 6
Clinical Approach to Identifying Secondary Causes
When evaluating an adult with membranous nephropathy, you must systematically exclude secondary causes before diagnosing primary MN. The KDIGO 2021 guidelines emphasize distinguishing primary from secondary disease, as this fundamentally changes management 1.
Key Diagnostic Considerations:
- Age matters: Secondary MN from malignancy is particularly important to consider in elderly patients 7
- Anti-PLA2R antibody status: While positive anti-PLA2R antibodies suggest primary MN (found in ~70% of primary cases), they can occasionally be positive even in secondary forms, creating diagnostic complexity 8, 9, 7
- Kidney biopsy remains essential when secondary causes are suspected, despite the availability of serologic markers 7
Important Clinical Pitfalls
Do not assume anti-PLA2R positivity excludes secondary disease entirely. Rare cases demonstrate PLA2R positivity alongside features of lupus nephropathy or other secondary causes 9, 7. In elderly patients with positive anti-PLA2R antibodies, consider the possibility of concurrent conditions like renal amyloidosis before initiating standard MN treatment 7.
The distinction between primary and secondary MN has profound implications for treatment and prognosis, as immunosuppressive regimens differ substantially between these categories 9, 7.