Unprovoked pulmonary embolism with bilateral deep vein thrombosis revealing occult nephrotic syndrome due to seronegative membranous nephropathy

Introduction: Nephrotic syndrome is a well-recognised risk factor for venous thromboembolism (VTE) but may present without oedema, hyperlipidaemia or impaired kidney function, delaying diagnosis. Case description: A 73-year-old man presented with fatigue, exertional dyspnoea and weight loss over a period of three months. Computed tomography pulmonary angiography showed bilateral central pulmonary emboli. Cardiac biomarkers were elevated with preserved renal function. Therapeutic anticoagulation was initiated. To assess thrombus extent and guide management, lower limb compression ultrasonography was performed and revealed bilateral popliteal deep vein thrombosis. Urinalysis demonstrated nephrotic-range proteinuria (8 g/day) with hypoalbuminaemia and microscopic haematuria. Evaluation for other secondary causes of thrombembolism was unremarkable. Anti-phospholipase A2 receptor and thrombospondin type-1 domain-containing 7A antibodies were negative. Corticosteroid treatment was commenced. A transjugular kidney biopsy confirmed membranous nephropathy, and rituximab was administered for long-term immunosuppressive management. Discussion: This case illustrates that nephrotic syndrome can be clinically occult and should be considered in unprovoked or extensive VTE, particularly when bilateral deep vein thrombosis is present. Conclusion: Urine dipstick testing, and serum albumin should be considered early in the work-up of unexplained VTE, even in the absence of oedema or reduced estimated glomerular filtration rate. LEARNING POINTS: Occult nephrotic syndrome can present with extensive or unprovoked venous thromboembolism despite normal estimated glomerular filtration rate and absent oedema - include urine dipstick testing and serum albumin early in the work-up.Lower limb compression ultrasonography can help define thrombus extent and guide management in pulmonary embolism. Bilateral deep vein thrombosis is uncommon and should prompt an expanded search for secondary causes.Negative anti-phospholipase A2 receptor and thrombospondin type-1 domain-containing 7A serology does not exclude membranous nephropathy. Kidney biopsy should be pursued when nephrotic-range proteinuria and hypoalbuminaemia are present.