Zinc-induced hemolytic anemia in a dog caused by ingestion of a game-playing die

Abstract

A 16-month-old spayed female mixed breed dog was presented with a 1-week history of anorexia, lethargy, diarrhea, vomiting, and difficulty rising. Hematologic evaluation indicated a marked macrocytic hypo-chromic, markedly regenerative anemia. A metallic foreign object in the gastrointestinal tract was identified on abdominal radiographs. Serum zinc concentration was markedly increased.

A 16-month-old spayed female mixed breed dog was presented to the Atlantic Veterinary College (AVC) Teaching Hospital with a 1-week history of anorexia, lethargy, vomiting, explosive diarrhea, and difficulty rising. The dog had been tentatively diagnosed with immune-mediated hemolytic anemia at a referring veterinary hospital but was not responding to corticosteroid therapy consisting of an initial intravenous injection of dexamethasone at 0.3 mg/kg body weight (BW) followed by 50 mg of prednisone orally (unknown dosage frequency and duration). One day prior to referral, abdominal radiographs were taken and a square metallic foreign object measuring approximately 3 × 3 cm was observed in the gastrointestinal tract. On route to the AVC Teaching Hospital, one of the owner’s children reported that they were missing a die from their poker dice set.

Case description

On presentation at the AVC Teaching Hospital, the patient was weak, depressed, and recumbent. Physical examination revealed tacky pale mucous membranes with a prolonged capillary refill time, tachycardia (140 beats/min), and tachypnea (44 breaths/min). Initial laboratory evaluation indicated a markedly decreased packed cell volume (PCV) [15%, reference interval (RI): 40% to 56%], and a mild hyperglycemia (9.1 mmol/L, RI: 3.3 to 5.6 mmol/L). Total protein, urea, and lactate concentrations were all within reference limits.

The patient was initially stabilized with a 350-mL bolus of intravenously administered fluid (Plasmalyte 148; Baxter, Deerfield, Illinois, USA) supplemented with 15 mEq/L of potassium chloride. Blood was drawn for a complete blood (cell) count (CBC), serum biochemical profile, and blood lead and zinc concentrations. This was followed by a 425-mL whole blood transfusion from a DEA 1.1 negative donor. A canine 4DX Snap test (IDEXX, Westbrook, Maine, USA) was performed; the results were negative. The CBC revealed a mild leukocytosis (24.7 × 10⁹/L, RI: 5.4 to 14.3 × 10⁹/L) characterized by a mild neutrophilia (17.9 × 10⁹/L, RI: 2.8 to 10.1 × 10⁹/L), a mild left shift (bands 1.9 × 10⁹/L, RI: 0.0 to 0.3 × 10⁹/L) with mild toxic change, moderate lymphopenia (0.5 × 10⁹/L, RI: 0.9 to 4.6 × 10⁹/L) and moderate monocytosis (3.6 × 10⁹/L, RI: 0.1 to 1.4 × 10⁹/L). These findings supported inflammation coupled with a stress or corticosteroid response, or both. The erythron indicated a marked anemia which was macrocytic, hypochromic, and markedly regenerative (red blood cell count 1.7 × 10¹²/L, RI: 5.7 to 8.4 × 10¹²/L; hemoglobin 30 g/L, RI: 135 to 198 g/L; hematocrit 0.13 L/L, RI: 0.40 to 0.56 L/L; mean corpuscular volume 77 fL, RI: 64 to 75 fL; mean corpuscular hemoglobin concentration 234 g/L, RI: 334 to 357 g/L; absolute reticulocyte count 695 × 10⁹/L, RI: 0 to 85 × 10⁹/L). No Heinz bodies, eccentrocytes, or spherocytes were observed. Platelets were clumped; however, based on blood smear evaluation, platelets were considered to be marginally decreased to potentially adequate (estimated at 182 to 230 × 10⁹/L, RI: 218 to 470 × 10⁹/L).

Initial serum biochemistry analysis revealed a moderate hypernatremia (163 mmol/L, RI: 144 to 151 mmol/L), moderate hyperchloremia (136 mmol/L, RI: 105 to 117 mmol/L), moderate increase in alkaline phosphatase activity (ALP) (549 U/L, RI: 18 to 113 U/L), mild increase in creatine kinase (CK) activity (353 U/L, RI: 44 to 249 U/L), mild hypoproteinemia (51 g/L, RI: 56 to 71), mild to moderate hypoalbuminemia (23 g/L; RI: 30 to 36 g/L), and marginal total hyperbilirubinemia (5 mmol/L, RI: 0 to 4 mmol/L). Serum iron concentration was within reference limits. The hypernatremia and hyperchloremia were attributed to dehydration due to excessive gastrointestinal water loss, with potential contribution from decreased water intake. The increase in ALP activity was likely due to induction by the previously administered corticosteroids but cholestasis and endogenous cortisol induction were also considered. Muscle enzyme leakage was deemed mild and attributed to recumbency, or hypoxia due to anemia, or both. The hypoproteinemia and hypoalbuminemia were considered likely due to gastrointestinal loss or decreased hepatic production, or both. Renal protein loss was thought to be less likely, but a urinalysis was not performed. The marginal hyperbilirubinemia likely reflected hemolysis but early or mild cholestasis was also possible.

Serum lead concentration was within the reference limit while the zinc concentration was markedly increased at 24.4 ppm (RI: 0.70 to 2.00 ppm). Abdominal radiographs were repeated to evaluate the location of the foreign object and to assess the need for emergency surgery. The radiographs revealed movement of the foreign object through the gastrointestinal tract with no evidence of obstruction. The foreign object progressed to the rectum and was manually removed approximately 11 h after admission. It consisted of a partially digested and markedly eroded game-playing die (Figure 1). Atomic absorption spectrophotometry (AAnalyst 800; Waltham, Massachusetts, USA) revealed the die to be comprised of approximately 78% zinc. The patient received famotidine (Apo-famotidine; Apotex, Toronto, Ontario), 0.5 mg/kg BW, IV, q24h and cephazolin (Cefazolin; Kundl, Austria), 22 mg/kg BW, IV, q8h for 6 d. Due to worsening anemia, a suspected physiological murmur and the presence of premature ventricular contractions (PVCs) believed to be related to myocardial hypoxia, an additional whole blood transfusion was administered on the day of admission. A moderate thrombocytopenia developed on the second day after admission. This and a mildly prolonged partial thromboplastin time (PTT) raised suspicion of early disseminated intravascular coagulation, prompting a plasma transfusion on the second day. With continued supportive care, the hematocrit increased and stabilized (0.30, 0.28, and 0.31 L/L on days 2, 3, and 6 post-admission, respectively). Cardiac abnormalities and most of the presenting clinical signs resolved, although weakness, knuckling of the paws, and ataxia were still present until discharge.

Figure 1.

Eroded game-playing die (left) manually removed from the patient’s rectum and adjacent normal die with an intact outer coating. Approximate size of each die = 3 cm³.

Serum biochemistry panels on days 2, 3, and 6 post-admission revealed initially markedly increased total bilirubin concentrations that dramatically declined (146, 68, and 16 mmol/L on days 2, 3, and 6, respectively, RI: 0 to 4 mmol/L). Markedly increased ALP activity was also seen on the same days (2262, 3936, and 3764 U/L on days 2, 3, and 6, respectively, RI: 18 to 113 U/L). Moderately increased amylase and lipase activities developed on day 6 post-admission (2536 U/L, RI: 324 to 1005 U/L and 1860 U/L, RI: 78 to 583 U/L). Despite these changes, the dog was eating well and able to walk: she was discharged with a guarded to fair prognosis 7 d after admission. For approximately 8 to 12 wk following discharge, variably mild degrees of ataxia were observed by the owners and referring veterinarian. Eighteen months after discharge the dog was reported to have made a full clinical recovery.

Discussion

Zinc is an essential element required for proper growth and development; it is present in approximately 200 metalloenzymes. Over 70 of these enzymes are required for protein, carbohydrate, lipid, and nucleic acid metabolism. Zinc can be found in many household items including calamine lotion, zinc oxide ointments, shampoos, paints, galvanized products used in fencing, metal pet kennels, and coating for nails as well as the nuts and bolts used on pet transport kennels (1,2). One-cent coins from the United States minted after 1982 are made predominantly of zinc with a copper coating (3). In Canada, pennies minted between 1997 and 1999 are composed of 98.4% zinc, while those produced before and after this period have almost no zinc (4). Once ingested, zinc is dissolved in a pH-dependent manner by gastric acid (5) to form soluble zinc salts which can be absorbed into the circulation and can cause direct mucosal irritation and ulceration.

Acute zinc toxicosis has been reported in dogs but not cats, likely due to the more discriminatory eating habits of cats. Zinc toxicosis has been associated with hemolytic anemia (3,6,7), pancreatitis (8,9), pancreatic fibrosis (10), signs of gastrointestinal dysfunction (11), and acute renal failure (2,12). The most common clinical signs include vomiting, lethargy, anorexia, diarrhea, and pigmenturia (11). The most consistent clinicopathologic findings include hyperbilirubinemia and a moderate to severe anemia that is often macrocytic, hypochromic, and regenerative (11). The anemia is hemolytic in origin, but the pathophysiology of zinc-induced hemolysis is not fully known. Inhibition of glutathione reductase and enzymes of the hexose-monophsophate-shunt pathway are likely involved (13). Functional lack of these enzymes allows erythrocytes to be more susceptible to oxidative damage. Oxidative damage typically results in the production of Heinz bodies, which are denatured clumps of precipitated hemoglobin that bind to the inner erythrocyte membrane surface. Heinz bodies can decrease erythrocyte deformability and may alter membrane permeability secondary to depletion of sulfhydryl group numbers, which results in premature erythrocyte phagocytosis (13). Interestingly, the presence of Heinz bodies associated with zinc toxicosis has been inconsistently reported. A recent review of zinc toxicosis in dogs reported Heinz bodies to be present in only 33% of 19 patients (11). While oxidative damage may explain part of the hemolytic process, it may not be the only mechanism involved.

Spherocytes have also been reported in some cases of zinc toxicosis (2,12,14). Their presence can make it difficult to differentiate a zinc-induced hemolytic anemia from an immune-mediated hemolytic anemia. Similar to Heinz bodies, spherocytes are inconsistently described and reported to be present in only approximately 20% of dogs with zinc toxicosis (11). When present, the degree of spherocytosis is typically mild. Patients with marked spherocytosis, as well as agglutination, should instead be more strongly suspected to have immune-mediated hemolytic anemia than zinc toxicosis.

Other clinicopathological abnormalities in zinc toxicosis can include increased aspartate aminotransferase (AST) activity, possibly due to muscle hypoxia or erythrocyte hemolysis, elevated serum urea concentration related to dehydration or gastrointestinal hemorrhage, and hyperamylasemia and hyperlipasemia due to pancreatic inflammation (11). Increases in these parameters were not observed initially in the patient reported here. Mild increases in AST activity were observed during the hospitalization period and were attributed to muscle enzyme leakage and hepatocellular leakage as both mild increases in CK and alanine transaminase activities were concurrently observed. Increases in all 3 of these enzymes resolved on day 6 post-admission. Elevated serum urea concentrations were not observed. A 2.5-fold increase in amylase and lipase was noted on the 6th day from admission and may have supported pancreatic inflammation associated with zinc toxicosis as previously reported (9). However, a concurrent CBC did not support inflammation and additional testing to identify pancreatitis was not performed. The increasing serum ALP activity observed during hospitalization was most likely due to induction by administered corticosteroids, although anemic hypoxia and cholestasis may have been contributory. Exact dosages and duration of corticosteroid treatment prior to referral are not known. However, even mild dosages of corticosteroids for short periods of time can induce increased ALP enzyme activity that persists for up to 3 wk after cessation (15). Prolongation of the PTT has also been reported in some dogs with zinc-induced hemolysis, possibly due to inhibition of intrinsic pathway coagulation factors (2,11). The prothrombin time (PT) is generally within reference limits. The dog in this report had a mildly prolonged PTT and a PT within reference limits.

In conjunction with typical clinicopathological findings, suspicion of zinc toxicosis is dramatically increased by finding metallic dense foreign objects on radiographic films. Objects are often present in the stomach or intestines but clinical suspicion of zinc toxicosis can be elusive if the patient has passed the foreign object in vomitus or feces prior to obtaining radiographs. As well, small zinc-coated objects with cores comprised of non-metallic materials may have their zinc coating eroded by stomach acids and be undetectable on survey radiographs. Topical zinc sources such as zinc oxide ointment are not radiographically detectable, reinforcing the importance of obtaining a thorough history. Definitive diagnosis requires finding elevated serum zinc levels. The reference interval for serum zinc in dogs is 0.7 to 2.0 ppm and most dogs with confirmed zinc toxicosis have zinc concentrations > 10 ppm. Blood should be collected into specific tubes with a royal blue rubber stopper for trace element measurement. Routine blood tubes such as lavender-topped tubes should be avoided as these can contribute up to 5.6 ppm of zinc to the sample (2). Serum red-topped tubes should also be avoided.

Removal of any ingested source of zinc by gastroendoscopy, gastrotomy, or enterotomy is critical to successful treatment. Blood transfusion is often required (11) and critical monitoring should include assessment of the coagulation status to detect localized or disseminated intravascular coagulation. Symptomatic and supportive care to correct and maintain hydration, electrolyte balance, and acid-base status are important. Although uncommon, acute renal failure is a potential sequela of zinc toxicosis, reiterating the significance of adequate renal perfusion (16). Gastrointestinal tract protectants, antiemetics, and antimicrobials are commonly instituted. Recent in vitro information supports the early administration of antacids (5). Aminoglycosides should be avoided due to their nephrotoxic potential. Chelation of zinc with calcium disodium EDTA has been described as a therapeutic option (9); however, its use is controversial since chelation treatment may actually increase intestinal absorption of zinc that has already entered the gastrointestinal tract. Although limited information was available for significant conclusions, a review of zinc toxicosis revealed 2 dogs treated with calcium EDTA that each had a considerably longer than median hospital stay (3 and 13 days longer) compared with 17 dogs that did not receive EDTA therapy (11). Daily monitoring of CBC, serum biochemical and urinalysis data, as well as serum zinc concentrations will help assess the success of treatment. Prognosis is good with early detection, supportive treatment, and removal of the zinc source. However, late detection or the development of sequela (or both), such as pancreatitis, acute renal failure, disseminated intravascular coagulation or hepatic necrosis can prolong hospitalization or potentially result in death.

Zinc toxicosis is a well-recognized yet uncommon source of hemolytic anemia in dogs. This report describes a case of severe hemolytic anemia associated with ingestion of a game-playing die composed predominantly of zinc. To the authors’ knowledge, ataxia has not been previously reported in dogs with zinc toxicosis and the origin of the ataxia in this case remains unknown. While whole blood lead concentrations were within reference limits and the foreign object was composed mainly of zinc (~78%), other substances present in the die potentially accounting for the ataxia cannot be ruled out. Similarly, localized intravascular coagulation leading to a potential thromboembolic event affecting the nervous system cannot be excluded. Blood smear findings from this dog were not strongly suggestive of zinc toxicosis, since evidence of oxidative damage such as Heinz bodies and eccentrocytes were not observed. The presence of the metallic foreign body on radiographs and the high serum zinc concentration allowed diagnosis of zinc toxicosis. Clinicians should be aware that zinc toxicosis is a cause of hemolytic anemia but that evidence of erythrocyte oxidative damage is frequently lacking on routine blood smears.