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Abstract: PO1948

Myoglobin Deposition in the Proximal Tubular Cells in a Patient with Dermatomyositis and Nonglomerular Proteinuria

Session Information

Category: Pathology and Lab Medicine

  • 1600 Pathology and Lab Medicine


  • Hammad, Dina, The University of Texas Rio Grande Valley, Edinburg, Texas, United States
  • Loftis, Christine E., The University of Texas Rio Grande Valley, Edinburg, Texas, United States
  • Varela, Daniel, The University of Texas Rio Grande Valley, Edinburg, Texas, United States
  • Alsabbagh, Mourad, DHR Health, Edinburg, Texas, United States
  • Mangi, Salil, DHR Health, Edinburg, Texas, United States

Dermatomyositis (DM) is a rare inflammatory myopathy characterized by proximal muscle weakness and skin lesions. Clinical manifestations of DM can involve any organ, including the kidneys. Although renal manifestations are rare, the literature describes cases of DM associated with mesangial proliferative glomerulonephritis, minimal change disease, Ig-A nephropathy, and acute tubular necrosis due to myoglobinuria. We report a rare case of DM with a predominant nonglomerular (NG) proteinuria, with kidney biopsy showing myoglobin deposition in the proximal tubules.

Case Description

A 38-year-old man presented with complaints of gradually worsening proximal muscle weakness and violaceous skin rash. Laboratory studies revealed an elevated creatinine phosphokinase (CPK) level of 8,250 IU/, 3+ hematuria with RBC 0-2, serum creatinine of 0.9 mg/dL, 24-hour urine test showed 1.8 g protein with 343 mg of albumin. The ANA titer was 1:1280, dsDNA was negative. A renal biopsy was done, and it showed acute tubular injury with increased proximal tubular cytoplasmic myoglobin staining with no myoglobin casts. There was no evidence of lupus nephritis. After corticosteroid therapy, Hydroxychloroquine, Mycophenolate Mofetil, and later Rituximab; his CPK level, proteinuria, and clinical symptoms have all steadily improved. This case demonstrates an atypical presentation of DM manifested by NG overflow proteinuria.


The main renal manifestations of polymyositis are acute kidney injury related to rhabdomyolysis and glomerulonephritis. Our case highlights a rare presentation of NG proteinuria with preserved renal function. The proteinuria likely resulted from myoglobin and impaired absorption of protein by the proximal tubular cells due to pathologic myoglobin deposition. There was no other evidence of proximal tubule impairment such as hypophosphatemia or glucosuria. In a study at Nephropath, looking at five hundred eighty kidney biopsies with myoglobin stain, most of the cases had myoglobin casts, with only 12 % of them having myoglobin deposition in the proximal tubular cells.