A 20–year–old African American Female was admitted with diffuse skin thickening and intractable pain in these skin lesions. Her past medical history was significant for recurrent kidney stones for which she had undergone bilateral nephrectomy a year previously and had been on renal replacement therapy. She was suffering from severe cachexia, tachycardia of 130 bpm, hypotension with BP of 90/64 mmHg, and her skin was thickened with contractures in her lower extremities. She had significant pain with passive movement. Her labs were significant for BUN of 80 mg/dL, Creatinine of 12.39 mg/dL, Calcium of 7.6 mg/dL, Phosphorus of 10.4 mg/dL, Albumin of 1.7 g/dL and PTH of 1601 pg/mL. She underwent a skin biopsy which showed calcinosis cutis. Previous records revealed renal stone analysis demonstrating calcium oxalate stones. Entertaining a diagnosis of primary hyperoxaluria, she underwent a liver biopsy and alanine glyoxylate aminotranferase (AGT) activity analysis was consistent with a diagnosis of Primary Hyperoxaluria (PH) type 1.
PH type 1 is related to a defect in the gene that encodes the hepatic peroxisomal enzyme AGT, which is involved in the conversion of glyoxylate to glycine. It accounts for about 80% of PH cases. The excess oxalate produced is mainly excreted by the kidneys which results in urinary calcium oxalate supersaturation with crystal aggregation and deposition in the renal interstitium resulting in nephrocalcinosis and recurrent urolithiasis often resulting in end–stage kidney failure. As GFR falls, calcium oxalate is deposited in other tissues including the retina, myocardium, vessel walls, skin, bone, and central nervous system. Calcinosis cutis is dystrophic calcification resulting from high calcium and phosphate product levels. A strong clinical suspicion is required as it is a rare disorder and the efficacy of treatment is dependent on early diagnosis. In cases of recurrent urolithiasis or nephrocalcinosis, if metabolic screening demonstrates increased urinary oxalate excretion, diagnosis of PH type 1 should be confirmed by genetic testing. Treatment modalities include increased fluid intake, avoidance of fluid with high oxalate concentration, enhancing oxalate elimination by gastrointestinal tract and use of high dose pyridoxine which facilitates conversion of glyoxylate to glycine, rather than to oxalate. Other options include using citrate or magnesium as an inhibitor of oxalate precipitation.
Primary hyperoxaluria is a rare inborn error of glyoxylate metabolism leading to overproduction of oxalate and deposition of calcium oxalate in various organs. This disorder can present further diagnostic challenge in patients in whom urinary testing is not possible after they have already suffered from anuria and renal failure due to recurrent stones or have undergone bilateral nephrectomy.