Zinc deficiency in adult patients with sickle cell disease was first reported in 1975. A variety of clinical manifestations of this disorder were then attributed to zinc deficiency. One of its rare clinical manifestation is hyperammonemia related encephalopathy.
A 50 year old African American female with known sickle cell disease and chronic renal disease, was admitted on the medical floor with nausea, vomiting and abdominal pain. Patient developed altered mental status requiring endotracheal intubation and transfer to intensive care unit (ICU). Patient’s vital signs on admission to ICU were stable. On physical examination the patient had grade IV encephalopathy. Pupils were 2 millimeters equal and reactive, corneal and gag reflexes were intact. The rest of the physical exam was unremarkable. Patient’s white blood cell count was 20 thousand per microliter, hemoglobin 7.3 milligram per deciliter (mg/dl) with hematocrit 20 percent. Alanine and aspartate aminotransferase were 94 and 134 International Units per Liter(IU/L) respectively. Alkaline phosphatase was normal and patient had evidence of hemolysis on laboratory data, which was at her baseline per her Hematologist. International normalized ratio was 1.7 and prothrombin time was 19 seconds. Electrolytes were in the normal range and she had baseline azotemia. During the course of her evaluation she was found to have an ammonia level of 437 micromoles per liter (αmol/L). Patient’s hepatitis profile was unremarkable and there was no history suggestive of alcohol consumption. Tylenol and Salicylate levels were non detectable. Ultrasound of liver and gallbladder revealed gall stones without inflammation, no hepatic or portal vein thrombosis. Viral serologies were negative. Analysis of cerebrospinal fluid was unremarkable. Computer tomography of the brain revealed cerebral edema. Electroencephalogram revealed generalized slowing. Zinc deficiency was also considered amongst other etiologies of hyperammonemia. The zinc level was found to be 50 microgram per deciliter. In addition to standard therapy with lactulose, zinc therapy was initiated and ammonia level started trending down. No other etiology for the hyperammonemia could be found in this patient. The mild elevation of liver function tests was attributed to the patient’s sickle cell disease and was at its baseline. Testing for inherited enzyme deficiency was not done, as the patient started showing clinical improvement after initiation of zinc therapy. Patient’s condition improved and she was ultimately transferred to a rehabilitation facility for further care.
Zinc deficiency has been reported to cause hyperammonemia in sickle cell patients. Several mechanisms have been proposed, including increase excretion of zinc due to impaired renal tubular handling. Also, zinc as a cofactor for ornithine transcarbamylase, a urea cycle enzyme, can inhibit the urea cycle and cause hyperammonemia. In addition, Deferoxamine in higher doses have been associated with increase fecal zinc excretion. However, more studies are needed to establish these causative relationships.
This case report documents hyperammonemia causing encephalopathy in a sickle cell disease patient that was corrected with zinc replacement therapy. Zinc deficiency should be considered as a cause of hyperammonemia and thus encephalopathy in patients with sickle cell disease.
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