Seizures Associated With Hypocalcemia in a Yorkshire Terrier With Protein-Losing Enteropathy

Introduction

Hypocalcemia has been a reported laboratory abnormality for dogs diagnosed with protein-losing enteropathy (PLE). However, these dogs do not typically exhibit clinical signs of this abnormality, such as muscle twitching, face-rubbing, or seizure activity. The purpose of this case report is to describe a case in which a middle-aged dog presented as an emergency for an acute onset of seizures due to hypocalcemia that occurred secondary to severe lymphangiectasia. Following treatment, including calcium supplementation and management for lymphangiectasia, the hypocalcemia and associated neurologic signs resolved.

Case Report

A 7 yr old, 5.4 kg (10.9 lb), neutered, male Yorkshire terrier was admitted to the emergency service at the Colorado State University College of Veterinary Medicine & Biomedical Sciences Veterinary Teaching Hospital approximately 1 hr after having a grand mal seizure. The dog appeared to be mildly disoriented at the time of examination, a finding attributed to a postictal period. The owners had also noticed that the dog had been pawing at its face both the day prior to and the day of presentation. Further review of the dog's history with the owner revealed an 18 mo history of vague, transient gastrointestinal signs, such selective appetite and abdominal distention and discomfort. These episodes would persist for 2–3 days and then spontaneously resolve. Starting 4 wk prior to presentation, the dog had begun vomiting bile-colored fluid approximately twice per wk and it had developed watery, voluminous stool consistent with small bowel diarrhea that occurred daily. The owners also reported that the dog became hyporexic 2 wk prior to presentation. Diagnostic testing performed by the primary care veterinarian for the progressive diarrhea and vomiting during the 6 wk prior to presentation included a complete blood count, serum chemistry, fecal flotation, and abdominal radiographs. No significant abnormalities of these diagnostic tests were noted, and previously measured serum protein levels had been normal. The primary care veterinarian prescribed famotidine (0.5 mg/kg per os [PO] q 12 hr) and instructed the owners to add fiber to the dog's diet for the small bowel diarrhea that had been occurring daily for 6 wk. On physical examination, the dog's temperature was 38.4°C, the heart rate was 126 beats per min, and the respiratory rate was 48 breaths per min. The mucous membranes were pink with a capillary refill time of less than 2 s, and the abdomen appeared to be distended. A packed cell volume was measured at 40% and the total solids were measured at 2.0 g/dL. A venous blood gas was also performed at the initial presentation. This revealed a marked ionized hypocalcemia (0.59 mm/L; reference range 1.19–1.48 mm/L). An intravenous catheter was placed and the dog was administered a bolus of 6 mEqs of calcium gluconate over 1 hr (1mEq/kg, IV, once). A continuous electrocardiogram was used to monitor heart rate and rhythm during the administration of the calcium gluconate. No abnormalities were noted. Following the administration of calcium gluconate, the dog was placed on an intravenous infusion of a balanced crystalloid solution^a with 20 mEq/L potassium chloride added (2.75 ml/kg/hr, IV) and a synthetic colloid^b (0.9 ml/kg/hr, IV). An ionized calcium level was measured three hr after the calcium gluconate was administered. The ionized calcium level had risen to slightly below normal range (1.18 mm/L). No additional seizure activity was observed following the administration of calcium gluconate. Due to the owner's financial concerns over additional hospitalization costs, the dog was discharged following initial assessment and stabilization, and a consultation with the internal medicine service was scheduled for later that same morning. In retrospect, continued hospitalization for ongoing intravenous calcium supplementation and monitoring would have been ideal given the severity of the hypocalcemia, and this should be considered in future cases. Ten hr after presentation as an emergency, the dog was returned for further examination and diagnostic testing through the internal medicine service. The owners did not report any seizure activity, but did note the dog exhibited several episodes of face rubbing during the discharge period.

Further diagnostics were performed at the time of the internal medicine referral. This included a complete blood count that revealed leukocytosis (27.2 × 10^3/ul; reference range 4.5–15.0 × 10^3/ul), neutrophilia (25.6 × 10^3/ul; reference range 2.6–11.0 × 10^3/ul), and increased bands (0.5 × 10^3/ul; reference range 0.0–0.4 × 10^3/ul). A mild lymphopenia was also noted (0.8 × 10^3/ul; reference range 1.0–4.8 × 10^3/ul). Platelets were elevated (943 × 10^3/ul; reference range 200–500 × 10^3/ul). A serum chemistry revealed marked total hypocalcemia (4.8 mg/dl; reference range 9.2–11.7 mg/dL), moderate hypomagnesemia (1.1 mg/dL; reference range 1.9–2.7 mg/dL), marked panhypoproteinemia (albumin, 1.2 g/dL [reference range 2.5–4.0 g/dL]; globulin, 1.1 g/dL [reference range 2.0–3.8 g/dL]), and hypocholesterolemia (68 mg/dL; reference range 130-300 mg/dL). Blood glucose, renal values, liver enzyme activity, and other major serum electrolytes (sodium, potassium, and chloride) were normal. Ionized calcium had dropped from 1.18 mmL to 0.73 mm/L over the 3 hr that had passed since the discharge from the emergency service. A urinalysis was unremarkable and a fecal flotation was negative for parasite ova. An abdominal ultrasound revealed hyperechoic changes of the adipose tissue of the mesentery, mild to moderate peritoneal effusion, and enlargement of the left and right limbs of the pancreas, both of which were heterogenous in appearance. Very small, hyperechoic speckles and faint striations were visualized within the mucosal layer of the small intestinal wall. Pancreatitis, inflammation of the mesentery, and possible dilated lacteals and inflammation within the mucosa of the small intestine were suspected based on the findings of the ultrasound. Oral calcitriol (45 ng/kg, PO, q 24 hr) and calcium carbonate (1 g/day divided, PO, q 12 hr) were prescribed in an effort to maintain adequate serum calcium levels. Clinical signs of hypocalcemia were not present, and recommendations for further hospitalization and monitoring were declined. The dog was discharged while further serologic testing was pending.

At a recheck examination performed 5 days after initial presentation, the owners reported some mild improvement in the dog's gastrointestinal signs. The abdomen was still distended, although the appetite appeared to be improving. No additional seizure activity or face rubbing had been observed since the discharge 5 days earlier. A packed cell volume was 40% and total solids were 4.4 g/dL. The total protein was 3.3 g/dL with an albumin of 1.6 g/dL. Ionized calcium was normal (1.24 mm/L). Fasting cobalamin was low (<150 ng/L; reference range 249–733 ng/L), fasting folate was normal (10.7 ng/L; reference range 6.5–11.5 ng/L), fasting pancreatic lipase immunoreactivity was elevated (431 ug/L; reference range 0–200 ug/L), and fasting trypsin-like immunoreactivity was normal (15.5 ug/L; reference range 5–35 ug/L). The elevated pancreatic lipase immunoreactivity was consistent with a diagnosis of pancreatitis, which had been previously suspected based on abdominal ultrasound. A parathyroid profile revealed an elevated parathyroid hormone (PTH) level (23.7 pmol/L; reference range 3–17 pmol/L) and a low ionized calcium level (0.73 nmol/L; reference range 1.25–1.45 nmol/L). A measurement of 25-hydroxyvitamin D was markedly low (7 nmol/L; reference range 60–215 nmol/L). The dog was discharged with instructions to continue the calcitriol and calcium carbonate. Based on the dog's signalment, its clinical signs of gastrointestinal disease, and its ultrasound findings, lymphangiectasia was suspected, and the dog was prescribed a fat-restricted diet^c and scheduled for an upper gastrointestinal endoscopy.

Nine days following initial presentation, the dog was returned for endoscopic examination and biopsy. A serum chemistry and ionized calcium measurement were performed prior to anesthesia. Serum total calcium was 6.3 mg/dL and magnesium was 1.3 mg/dL. Albumin and globulins were still decreased (1.5 g/dL and 1.3 g/dL, respectively). Ionized calcium was decreased at 1.01 mm/L. Despite the persistent moderate ionized hypocalcemia, the dog was stable, and there were no neurologic manifestations of abnormal calcium levels. During the endoscopy, the esophageal and gastric mucosal surfaces appeared grossly normal. The mucosa of the duodenum had an abnormal, roughened, proliferative, nodular appearance. Grayish-white nodules and debris were visualized within the lumen, and the mucosa was very friable. Histopathology revealed mild lymphoplasmacytic enteritis with dilated lacteals consistent with inflammatory bowel disease and lymphangiectasia. Based on the results of the serum chemistry and biopsies, magnesium sulfate (2.5 mEq/dog, PO, q 12 hr), rutin (250mg/dog, PO, q 8 hr), and prednisone (1.0 mg/kg, PO, q 12 hr) were prescribed. Calcitriol, calcium carbonate, and dietary management with a fat-restricted diet were continued.

Nine days following endoscopy, and 18 days after initial presentation, the dog presented for re-evaluation. The owners reported that the dog was improving, its appetite was better, its stools were formed, and it had not had any seizures or face rubbing. Serum total calcium was elevated at 12.9 mg/dL and ionized calcium was elevated at 1.60 mm/L. Serum magnesium, albumin, globulins, and cholesterol were within the reference rage (2.4 mg/dL, 2.5 g/dL, 2.2 g/dL, and 117 mg/dL, respectively). The calcitriol was tapered (45 ng/kg [20 ng/kg], PO, q 48 hr) and calcium carbonate and magnesium sulfate were discontinued. The owners were instructed to continue the prednisone, rutin, and low-fat diet. The dog was also given an injection of vitamin B12 (250mg, subcutaneously).

Twenty-three days after initial presentation, the dog was re-examined. The dog's clinical signs had continued to improve according to his owners. The serum total calcium was normal at 10.2 mg/dL and ionized calcium was slightly decreased at 1.15 mm/L. Albumin and globulin levels were normal (3.1 g/dL and 2.3 g/dL, respectively). The owners were instructed to continue the medications and dietary management as previously directed.

The dog's next recheck occurred 7 wk after his initial presentation for seizures. The owners reported it was doing well. Calcium and albumin were within normal reference range and globulins were slightly decreased (10.4 mg/dL, 3.2 g/dL, and 1.8 g/dL, respectively). The dog's owners were directed to continue the low-fat diet. Prednisone was tapered to 1mg/kg, PO, q 24 hr, the rutin dose was decreased by 50%, and calcitriol was discontinued. The dog also received an additional injection of vitamin B12 (250mg, subcutaneously).

Three mo after initial presentation, another recheck was performed. Clinically, the dog was doing well with no relapses of vomiting, diarrhea, seizures, or face rubbing. Serum and ionized calcium levels were normal (10.5 mg/dL and 1.32 mm/L, respectively), despite a complete discontinuation of oral calcium and vitamin D supplementation. Albumin and globulins were within normal reference range (3.6 g/dL and 2.1 g/dL, respectively). Prednisone was tapered to 0.5mg/kg, PO, every other day, and rutin was decreased from every 8 hr to every 12 hr. Follow up monitoring at 6, 16, and 36 mo after initial presentation revealed normal calcium levels (10.8 mg/dL, 11.0 mg/dL, and 11.0 mg/dL, respectively) and normal albumin and globulin levels.

One year after initial diagnosis, the dog was transitioned from prednisone to budesonide to minimize systemic effects of glucocorticoid therapy, such as polyuria and polydipsia. The dog continued to do well with routine monitoring and treatment for inflammatory bowel disease and lymphangiectasia, including budesonide, rutin, and a low-fat diet. Its serum chemistry panel remained normal, and it did not require any further calcium or vitamin D supplementation. The dog was eventually euthanized 4.5 yr after initial presentation for an unrelated illness.

Discussion

Intestinal lymphangiectasia is a form of protein-losing enteropathy characterized by the disruption of normal lymphatic flow. As lymph flow is disrupted, leakage of protein-, lipid-, and lymphocyte-rich fluid into the lumen of the intestine occurs. This results in marked systemic panhypoproteinemia, lymphopenia, and hypocholesterolemia. Dogs with lymphangiectasia commonly present due to signs of gastrointestinal upset or consequences of these abnormalities, including pleural effusion, peritoneal effusion, and pitting edema of the extremities.

It is suspected that lymphangiectasia most commonly occurs as a result of inflammatory disease of the gastrointestinal tract, and there are reports of an increased incidence of lymphangiectasia in association with the presence of moderate to severe lymphocytic-plasmacytic enteritis. It may also occur secondary to congenital malformation of lymphatic vessels as well as obstruction of the lymphatic vessels due to fibrosis, neoplasia, and heart failure.^1,2

Hypocalcemia has been reported in association with various forms of protein-losing enteropathies, including lymphangiectasia. Decreases in total calcium are often seen in association with hypoalbuminemia. In many cases, the hypocalcemia is mild to moderate in nature, the ionized calcium levels are normal, and clinical signs attributable to hypocalcemia are not observed.^2–4 Studies have speculated that an additional factor involved with protein-losing enteropathies that may contribute to hypocalcemia is the decreased absorption of fat-soluble vitamin D through the intestinal mucosa.^2,3 An additional study also found that canine patients with protein-losing enteropathy had greater decreases in serum 25-hydroxyvitamin D concentrations compared to dogs with inflammatory bowel disease, dogs with non-intestinal illnesses, and a control group of healthy dogs. There was also a strong correlation between the 25-hydroxyvitamin D concentrations and alubumin concentrations in dogs with protein-losing enteropathy in the same study, thus suggesting that dogs with protein-losing enteropathy are at risk for developing hypovitaminosis D due to the loss of protein-bound vitamin D through the gastrointestinal tract.⁵ Normally, following absorption in the intestine, vitamin D is metabolized to 25-hydroxyvitamin D and then to its active form, 1,25-dihydroxyvitamin D (calcitriol), by the liver and kidneys, respectively. Poor intestinal absorption and increased loss of vitamin D within the intestinal tract ultimately will result in low serum levels of 1,25-dihydroxyvitamin D, leading to decreased bone resorption and decreased intestinal absorption of calcium. In these cases, not only the total calcium but also the ionized calcium is expected to be low.^5–7

Approximately 99% of the body's calcium stores lie in bone. Of the remaining 1% within the extracellular fluid space, 50% of calcium is in its ionized, active form; 40% is bound to plasma proteins; and 10% is in a non-ionized form.^3,6,7 Common causes for hypocalcemia in the dog include primary hypothyroidism, chronic or acute renal failure, hypoalbuminemia, acute pancreatitis, eclampsia, malabsorption syndromes, nutritional secondary hypoparathyroidism, and phosphate over-supplementation. Less common etiologies include alterations of total body magnesium levels, hypovitaminosis D, tumor lysis syndrome, and over-administration of certain anticoagulants, such as EDTA or citrate that bind or chelate calcium. Neurologic manifestations of hypocalcemia include seizures, muscle tremors, face rubbing, and changes in attitude. Face rubbing and behavioral changes are attributed to discomfort caused by muscle spasms or cramping.^7–9 Clinical manifestations of hypocalcemia are reported to occur at serum total calcium concentrations below 6–7 mg/dL and serum ionized calcium concentrations below 0.7–0.8 mmol/L.^7–8

Clinically significant hypocalcemia associated with protein-losing enteropathies in dogs has been reported in veterinary medicine. However, the majority of these dogs were initially presented for various signs of gastrointestinal disease (vomiting, diarrhea, weight loss, and anorexia). Signs of hypocalcemia, including weakness, tremors, and owner-reported seizure activity, have been reported in association with these cases as secondary complaints only.^3,4,10 To the authors' knowledge, the case reported here is the first in which a dog with a PLE was presented with the primary complaint of grand mal seizures.

The development of acute neurologic signs secondary to hypocalcemia has been reported in human cases of protein-losing enteropathy. Two separate case reports have documented the occurrence of grand mal seizure events in young children that also had concurrent gastrointestinal signs, including small bowel diarrhea, vomiting, and poor weight gain. Both dogs were diagnosed with lymphangiectasia, and, in each case, hypocalcemia, panhypoproteinemia, and hypomagnesemia were identified laboratory abnormalities. Following appropriate treatment of the underlying lymphangiectasia, correction of hypocalcemia, and correction of plasma protein concentrations, both dogs recovered, their respective serum calcium levels normalized, and no further neurologic signs persisted.^11,12

In both human and veterinary literature, the serum magnesium level has been shown to have an important effect on serum calcium, PTH, and 1,25 dihydroxyvitamin D levels. Hypomagnesemia can result from loss through the kidneys, loss through the gastrointestinal tract, a dietary deficiency, or a change in magnesium distribution as a result of administration of glucose, insulin, or amino acids. In one published study, a 5 yr old shih tzu presented for a history of lethargy, paresis, and abdominal distention of 2 wk duration. The dog was hypocalcemic, panhypoproteinemic, and hypomagnesemic. A serum PTH level was also reported to be low. It was concluded that the decrease in serum magnesium level resulted in a pronounced drop in serum PTH levels through a decrease in modulation of adenylate cyclase, an enzyme involved in the production of cyclic adenosine monophosphate, which stimulates the release of PTH from the parathyroid gland. This drop in PTH, in addition to the loss of albumin and malabsorption of vitamin D secondary to the lymphangiectasia, resulted in the dog becoming hypocalcemic.¹⁰ It has also been shown that hypomagnesemia can decrease the magnitude of the effect of PTH on its target tissues, thus contributing to disruptions of calcium homeostasis.⁴ Despite initial hypomagnesemia (1.1 mg/dL; reference range 1.9–2.7 mg/dL), PTH levels were increased in the dog of this report. Therefore, it is unlikely that hypomagnesemia contributed to the hypocalcemia reported here.

Alterations in coagulability have been documented in dogs with PLE. A prospective study evaluating both thromboelastography and serum antithrombin concentrations in dogs with confirmed PLE did show that a hypercoagulable state exists in dogs with PLE compared to a control group of healthy dogs.¹³ In this study, dogs with PLE had significant thromboelastography alterations indicative of hypercoagulability and low-normal antithrombin levels. Clinical relevance of this hypercoagulable state has been established through a case report of a dog with confirmed PLE that died as a result of a pulmonary thromboembolism.¹⁴ Speculation exists that hypocoagulability could be associated with PLE in dogs due to vitamin K malabsorption with prolongation of prothrombin time and activated partial thromboplastin time, but this has not been confirmed through other studies.^3,4 Assessment of prothrombin time and activated partial thromboplastin time were discussed and recommended for the dog in this case report, but were declined due to financial concerns by the owner. Despite the lack of the prescription of antithrombotics to the dog in this case study, a successful outcome was achieved. Current recommendations for dogs with PLE include prophylactic treatment for hypercoagulability with appropriate antithrombotic medications.

Conclusion

The concept of hypocalcemia resulting from protein-losing enteropathy is not novel. However, until recently, the magnitude and clinical significance of these decreases in calcium were thought to be mild in nature and did not warrant attention or specific treatment beyond management of the underlying intestinal disease. While dogs with severe malabsorptive disease much more commonly present with primary gastrointestinal signs, malabsorptive disease should also be considered as a differential diagnosis in dogs exhibiting neurologic signs, hypocalcemia, and hypoalbuminemia.