A unique case of light chain (AL) amyloidosis masquerading as hypophosphatemic osteomalacia
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CASE REPORT
A unique case of light chain (AL) amyloidosis masquerading as hypophosphatemic osteomalacia R. Malhotra 1
&
P. Guleria 2 & A. Barwad 2 & R. Pramanik 3 & N. Tandon 1
Received: 10 June 2020 / Accepted: 1 September 2020 # International Osteoporosis Foundation and National Osteoporosis Foundation 2020
Abstract Light chain (AL) amyloidosis is the result of a clonal plasma cell disorder which causes organ damage by deposition of misfolded light chains. Kidney is a common site of amyloid deposition. Proteinuria, usually in nephrotic range and unexplained renal insufficiency are the main manifestations of renal injury. We report a unique case of renal involvement by AL amyloidosis masquerading as metabolic bone disease. 38 year old male patient presented with progressively increasing diffuse bony pains, low backache and proximal weakness of both lower limbs since two years. On investigation, he was detected to have hypophosphatemic osteomalacia due to renal phosphate loss which was fibroblast growth factor 23 (FGF23)- independent. He also had nephrotic range low molecular weight proteinuria. Renal biopsy to ascertain the aetiology revealed deposition of amyloid fibrils in the glomerular mesangium on electron microscopy. Its characterization by immunofluorescence (IF) was consistent with immunoglobulin light chain (AL) amyloidosis. In the absence of a demonstrable plasma cell clone on bone marrow biopsy, we made a diagnosis of monoclonal gammopathy of renal significance (MGRS). He was treated with chemotherapy following which there was symptomatic improvement and reduction in phosphaturia. This case describes a unique presentation of renal injury due to AL amyloidosis masquerading as hypophosphatemic osteomalacia. The aim of this report is to highlight that hypophosphatemia in adults is usually acquired and treatment of underlying etiology results in cure, unlike in children where genetic counseling and phosphate replacement is the mainstay of treatment. Key words AL amyloidosis . Fanconi syndrome . Fibroblast growth factor 23 . Hypophosphatemic osteomalacia . Monoclonal gammopathy of renal significance
Introduction The systemic manifestations of light chain (AL) amyloidosis are protean and are usually a consequence of advanced organ damage. Proteinuria is the most common manifestation of renal injury by amyloid deposition. Metabolic bone disease due to hypophosphatemia, as the initial manifestation of renal amyloidosis, has not been reported earlier. We report a rare
* R. Malhotra [email protected] 1
Department of Endocrinology and Metabolism, All India Institute of Medical Sciences, New Delhi, India
2
Department of Pathology, All India Institute of Medical Sciences, New Delhi, India
3
Department of Medical Oncology, All India Institute of Medical Sciences, New Delhi, India
case of AL amyloidosis presenting with bony pains and proximal myopathy due to renal tubular phosphate loss.
Case description A 38-year-old male security guard presented with a history of diffuse bony pains, low backache
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