Case#3
Clinical History
A 55 year old man who presented to emergency room with black stool, coffee ground emesis and acute kidney injury. Serum creatinine is 17.4 mg/dL. Creatinine kinase (CK) is 9874 U/L. Serum albumin is 2.3 g/L. ANA is negative. C3 is normal. C4 is slightly high. Kappa to lambda free light ratio is normal. There is no monoclonal protein by immunofixation. Urinalysis shows more than 600 protein, 18 white blood cells, and 3 RBCs.
Pathologic Examination
Light Microscopy Examination
H&E X6
Renal tubules show acute injury with simplified epithelium and ectatic lumina separated by interstitial edema. Hypereosinophilic casts can be seen within renal tubules.
PAS X16
Section shows that the casts are negative with PAS special stain
Trichrome X16
Trichrome special stain highlights the casts in bright red beaded like morphology
Immunofluorescence Studies
IgA
The casts are negative
Kappa
The casts are negative
Lambda
The casts are negative
Immunohistochemical Studies
Myoglobin Immunostain
The casts are strongly positive
Hemoglobin Immunostain
The casts are negative
Electron Microscopy
Ultrastructure of Myoglobin Casts
On electron microscopy, the tubular pigmented cast is composed of electron-dense myoglobin globule
Myoglobin cast nephropathy
KEY FACTS
Terminology
Acute renal failure associated with pigmented tubular casts due to myoglobinuria
Etiology/Pathogenesis
Rhabdomyolysis (injury to skeletal muscle) releases myoglobin, which is iron-containing skeletal muscle protein
Trauma, drugs, toxins, inherited metabolic disorders, inflammatory myopathies
Predisposing factors include dehydration, fasting, hypo- or hyperthermia, hypoxia, hypokalemia
Clinical Issues
• Acute renal failure
• Elevated creatine kinase (CK-MM, often > 100,000 IU/L)
Peaks within 48 hours after rhabdomyolysis with half-life of 48 hours
• Treatment is supportive with hydration
DIFFERENTIAL DIAGNOSIS
Bile Cast Nephropathy
• Severe liver dysfunction, usually with jaundice
• Casts appear identical to myoglobin or hemoglobin
Myeloma Cast Nephropathy
• Fractured casts, which are light chain restricted on immunofluorescence microscopy
Acute (Ischemic or Toxic) Tubular Necrosis
• Pigmented casts from mitochondrial cytochromes lack myoglobin or hemoglobin
