Diagnostic Work Up for Dogs with Hypercalcemia of Unknown Origin

My patient is an 8-year old spayed female mixed-Labrador that presented with marked polydipsia and polyuria. Otherwise, she appears to be feeling well; she has a normal appetite, with no weight loss, vomiting, diarrhea, or coughing.

Her initial work-up identified a high total serum calcium of 13.7 mg/dl (reference interval, 8.9-11.4 mg/dl), which was confirmed two days later (repeat calcium, 13.1 mg/dl). The rest of the serum biochemical analysis (including the serum sodium, potassium, urea nitrogen and creatinine) were normal. The results of a complete blood count were normal and a complete urinalysis was also unremarkable, except for a low urine specific gravity (1.010).

Chest and abdominal radiographs were normal.

A complete calcium panel was next performed (1), with the following results:

• Serum ionized calcium (iCa) = 1.63 mmol/L (reference interval, 1.25-1.45)
• Serum parathyroid hormone (PTH) = 1.0 pmol/L (0.5 - 5.8)
• Plasma parathyroid hormone-related polypeptide (PTHrp) = 0.3 pmol/L (<0.5)

How would you recommend that I proceed in the workup of this dog? I'm considering an abdominal ultrasound and bone marrow exam to look for occult lymphoma, and maybe a trial response to asparaginase?

My Response:

In adult dogs with repeatable hypercalcemia, the two most common causes include primary hyperparathyroidism and malignancy (2,3). Most dogs with primary hyperparathyroidism feel good (normal attitude and appetite), whereas those with hypercalcemia of malignancy tend to be clinically ill (4-7).  With the low-normal serum PTH value and measurable (but normal) PTHrp value, neither of those categories can be completely excluded (2,3,8).

With the current assay for PTH employed at DCPAH (1), it's been my observation that a serum PTH value higher than 1 pmol/L is generally consistent with primary hyperparathyroidism and a PTH value lower than 1 is consistent with PTH-independent hypercalcemia (usually neoplasia).  However, remember that PTH is a peptide and is subject to breakdown and degradation during shipping, especially if the plasma sample was not kept frozen or at least cool.  Therefore, sample handling issues (delay in transit or sample warming) can result in falsely-low serum PTH concentration. If there is any doubt about the sample integrity when it arrived in the lab, a new serum sample should be collected to recheck the PTH concentration. After the serum is collected, it should be immediately frozen and shipped by overnight delivery to the lab (with dry ice or freezer pack) to ensure valid results.

Hypercalcemia associated with Addison's disease is also relatively common in dogs and is possible in this case (9). However, the normal serum concentrations of sodium and potassium and the fact that your dog is not showing signs of serious illness make hypoadrenocorticism unlikely.  Most of these hypercalcemic dogs have overt Addison's disease, with moderate to marked hyperkalemia and hyponatremia.  That said, you could certainly run a resting cortisol concentration to help exclude hypoadrenocorticism — the finding of a serum cortisol value above 2.0 µg/dl basically rules out Addison's disease (10).

Rare causes of hypercalcemia also include hypervitaminosis D or A and granulomatous disease, so these must be considered (2,3,11,12). Most of the other differentials can be excluded with routine serum biochemical analysis and history (Table 1).

Table 1: Differential list for hypercalcemia in dogs

Workup for undefined hypercalcemia

There are a number of ways to handle this case. Here is a workup list for you to consider, starting with the easiest and least invasive:

1. Perform thorough rectal exam to rule out an anal sac adenocarcinoma (13-15).
2. Carefully check for lymph node enlargement and aspirate any lymph nodes that you can palpate.
3. Measure a resting cortisol concentration to help exclude hypoadrenocorticism. If the basal cortisol concentration is low, this should be followed up with an ACTH stimulation test to confirm Addison's disease (10).
4. Consider repeating the serum PTH concentration. Since lipemia can effect the results, the dog should be fasted overnight. After blood collection, allow serum to clot at room temperature for 30 to 60 min prior to separation. The serum sample should be immediately frozen and shipped by overnight delivery to the lab (with dry ice or freezer pack) for PTH analysis (1).
5. If the repeat PTH value is above 1.0 pmol/L (in other words, not suppressed) consider having an experienced radiologist perform a cervical ultrasound exam looking for a parathyroid nodule, which would more strongly suggest primary hyperparathyroidism (16).  
6. If the repeat PTH value is suppressed or if the cervical ultrasound fails to detect a parathyroid tumor, then consider a complete abdominal ultrasound examination to screen for possible occult cancer, especially lymphoma.
7. Collect multiple aspirates of the liver and spleen with ultrasound-guidance, even if those organs appear normal on your ultrasound exam. I've had cases in which the ultrasound exam appears normal but the cytology said otherwise.
8. Consider a bone marrow aspirate. However, given the normal hematology results, this is less likely to be diagnostic.
9. Finally, if all of the above fails to yield a definitive diagnosis, then consider monitoring the ionized calcium and PTH concentrations to make sure that the hypercalcemia does not rapidly progress and that the PTH value remains stable.  If the PTH value increases to the mid-normal to high range, that finding would be most consistent with primary hyperparathyroidism; on the other hand, if the value falls further, that would be consistent with PTH-independent hypercalcemia (e.g., malignancy) (2,3).

Bottom Line

If nothing is found on your complete workup, I've learned that close observation and monitoring is sometimes the best route to take.  This includes periodic exams (including lymph node palpation and rectal exams), as well as following the serum iCa concentrations. I've had a few dogs with persistent, but stable, idiopathic hypercalcemia in which a definitive cause for the hypercalcemia was never identified. But the dogs (and eventually the owners) didn't care all that much, since the degree of hypercalcemia remains fairly stable and was not very progressive.

By contrast, in those dogs that have progressive disease and develop severe, worsening hypercalcemia, the underlying cause will eventually be obvious, even if it isn't apparent during the initial workup.

References:

1. Michigan State University, Diagnostic Center for Population and Animal Health (DCPAH).
   4125 Beaumont Road, Lansing, MI 48910-8104. 
2. Schenck PA, Chew DJ. Investigation of hypercalcaemia and hypocalcaemia. In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology, Fourth ed. Quedgeley, Gloucester: British Small Animal Veterinary Association; 2012:221-233.
3. Skelly BJ. Hyperparathyroidism. In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Quedgeley, Gloucester: British Small Animal Veterinary Association; 2012:43-55.
4. Jores K, Kessler M. Primary hyperparathyroidism in the dog. Diagnosis, therapy and postoperative management in 19 dogs. Tierarztliche Praxis Ausgabe K, Kleintiere/Heimtiere 2011;39:389-396.
5. Schaefer C, Goldstein RE. Canine primary hyperparathyroidism. Compend Contin Educ Vet 2009;31:382-390.
6. Bergman PJ. Paraneoplastic hypercalcemia. Top Companion Anim Med 2012;27:156-158.
7. Vasilopulos RJ. Humoral hypercalcemia of malignancy: Diagnosis and treatment. Compend Contin Educ Vet 2003;25.
8. Rosol TJ, Nagode LA, Couto CG, et al. Parathyroid hormone (PTH)-related protein, PTH, and 1,25-dihydroxyvitamin D in dogs with cancer-associated hypercalcemia. Endocrinology 1992;131:1157-1164.
9. Peterson ME, Feinman JM. Hypercalcemia associated with hypoadrenocorticism in sixteen dogs. J Am Vet Med Assoc 1982;181:802-804.
10.  Lennon EM, Boyle TE, Hutchins RG, et al. Use of basal serum or plasma cortisol concentrations to rule out a diagnosis of hypoadrenocorticism in dogs: 123 cases (2000-2005). J Am Vet Med Assoc 2007;231:413-416.
11. Mellanby RJ, Mee AP, Berry JL, et al. Hypercalcaemia in two dogs caused by excessive dietary supplementation of vitamin D. J Small Anim Pract 2005;46:334-338.
12. Dow SW, Legendre AM, Stiff M, et al. Hypercalcemia associated with blastomycosis in dogs. J Am Vet Med Assoc 1986;188:706-709.
13. Williams LE, Gliatto JM, Dodge RK, et al. Carcinoma of the apocrine glands of the anal sac in dogs: 113 cases (1985-1995). J Am Vet Med Assoc 2003;223:825-831.
14. Meuten DJ, Capen CC, Kociba GJ, et al. Hypercalcemia of malignancy: Hypercalcemia associated with an adenocarcinoma of the apocrine glands of the anal sac. Am J Pathol 1982;108:366-370.
15. Hause WR, DVM, Stevenson S, DVM, MS, Meuten DJD, et al. Pseudohyperparathyroidism associated with adenocarcinomas of anal sac origin on four dogs. J Am Anim Hosp Assoc 1981;17:373-379.
16. Wisner ER, Penninck D, Biller DS, et al. High-resolution parathyroid sonography. Vet Radiol Ultrasound 1997;38:462-466.

Top Endocrine Publications of 2013: Canine & Feline Parathyroid & Calcium Disorders

In my third compilation of the canine and feline endocrine publications of 2013, I’m moving on to disorders of the parathyroid gland, including the clinical problems of hypercalcemia and hypocalcemia.

Listed below are 21 research papers written in 2013 that deal with a variety of topics and issues related to calcium, parathyroid or vitamin D metabolism.

These range from the interactions of calcitriol, calcidiol, parathyroid hormone, and fibroblast growth factor-23 in the pathogenesis of chronic kidney disease (1) to a number of reports of dogs with hypercalcemia of malignancy (2,4,5,7,16); from a review of hypocalcemia associated with critical illness (3) to a case of reversible myocardial failure associated with primary hypoparathyroidism in a cat (6); from a study of preoperative factors that help predict iatrogenic hypoparathyroidism following parathyroid surgery (8) to reviews of the emergency management of common metabolic abnormalities, including hypocalcemia, in cats that present with collapse (9,10); and from a study of the forms of dietary potassium in the prevention of calcium oxalate urolith formation in cats (11) to the effect of bone meal on urinary calcium and oxalate excretion in cats (12).

Other papers include a review of cholecalciferol (vitamin D3) intoxication leading to hypercalcemia (13) to changes in serum concentrations of calcium, phosphorus, magnesium, parathyroid hormone, calcidiol and calcitriol in growing cats (14) to a study of the plasma calcitonin response associated with hypocalcemia in cats (15); from a study of the vitamin D status in dogs with non-neoplastic and neoplastic esophageal nodules resulting from the nematode spirocercosis (17) to a case report of hypercalcemia secondary to Addison's disease in a cat (18); and finally, from a report of 3 cats with severe hypercalcemia secondary to vitamin D intoxication caused by ingestion of commercial cat foods (19) to a case report of a Persian cat that developed hypercalcemia secondary to intra-abdominal fungal pseudomycetoma (i.e., dermatophyte penetration into the abdominal cavity) (21) .

References:

1. de Brito Galvao JF, Nagode LA, Schenck PA, et al. Calcitriol, calcidiol, parathyroid hormone, and fibroblast growth factor-23 interactions in chronic kidney disease. J Vet Emerg Crit Care (San Antonio) 2013;23:134-162. 
2. Geigy C, Riond B, Bley CR, et al. Multiple myeloma in a dog with multiple concurrent infectious diseases and persistent polyclonal gammopathy. Vet Clin Pathol 2013;42:47-54. 
3. Holowaychuk MK. Hypocalcemia of critical illness in dogs and cats. Vet Clin North Am Small Anim Pract 2013;43:1299-1317, vi-vii. 
4. Javanbakht J, Tavassoli A, Sabbagh A, et al. Evaluation of an anal sac adenocarcinoma tumor in a Spitz dog. Asian Pac J Trop Biomed 2013;3:74-78. 
5. Javanbakht J, Tavassoli A, Sasani F, et al. An overall assessment of circumanal gland adenoma in a terrier mix breed dog. Asian Pac J Trop Biomed 2013;3:580-583. 
6. Lie AR, Macdonald KA. Reversible myocardial failure in a cat with primary hypoparathyroidism. J Feline Med Surg 2013;15:932-940. 
7. Merrick CH, Schleis SE, Smith AN, et al. Hypercalcemia of malignancy associated with renal cell carcinoma in a dog. J Am Anim Hosp Assoc 2013;49:385-388. 
8. Milovancev M, Schmiedt CW. Preoperative factors associated with postoperative hypocalcemia in dogs with primary hyperparathyroidism that underwent parathyroidectomy: 62 cases (2004-2009). J Am Vet Med Assoc 2013;242:507-515. 
9. Murphy K, Hibbert A. The flat cat: 1. a logical and practical approach to management of this challenging presentation. J Feline Med Surg 2013;15:175-188. 
10. Murphy K, Hibbert A. The flat cat: 2. the emergency database and management of common metabolic abnormalities. J Feline Med Surg 2013;15:189-199. 
11. Passlack N, Brenten T, Neumann K, et al. Effects of potassium chloride and potassium bicarbonate in the diet on urinary pH and mineral excretion of adult cats. Br J Nutr 2013:1-13. 
12. Passlack N, Zentek J. Urinary calcium and oxalate excretion in healthy adult cats are not affected by increasing dietary levels of bone meal in a canned diet. PLoS One 2013;8:e70530. 
13. Peterson ME, Fluegeman K. Cholecalciferol. Topics in companion animal medicine 2013;28:24-27. 
14. Pineda C, Aguilera-Tejero E, Guerrero F, et al. Mineral metabolism in growing cats: changes in the values of blood parameters with age. J Feline Med Surg 2013;15:866-871. 
15. Pineda C, Aguilera-Tejero E, Raya AI, et al. Assessment of calcitonin response to experimentally induced hypercalcemia in cats. Am J Vet Res 2013;74:1514-1521. 
16. Robat CS, Cesario L, Gaeta R, et al. Clinical features, treatment options, and outcome in dogs with thymoma: 116 cases (1999-2010). J Am Vet Med Assoc 2013;243:1448-1454. 
17. Rosa CT, Schoeman JP, Berry JL, et al. Hypovitaminosis D in dogs with spirocercosis. J Vet Intern Med 2013;27:1159-1164. 
18. Sicken J, Neiger R. Addisonian crisis and severe acidosis in a cat: a case of feline hypoadrenocorticism. J Feline Med Surg 2013;15:941-944. 
19. Wehner A, Katzenberger J, Groth A, et al. Vitamin D intoxication caused by ingestion of commercial cat food in three kittens. J Feline Med Surg 2013;15:730-736. 
20. Williams TL, Elliott J, Berry J, et al. Investigation of the pathophysiological mechanism for altered calcium homeostasis in hyperthyroid cats. J Small Anim Pract 2013;54:367-373. 
21. Zafrany A, Ben-Oz J, Segev G, et al. Successful treatment of an intra-pelvic fungal pseudomycetoma causing constipation and hypercalcaemia in a Persian cat. J Feline Med Surg 2013. 

Intraoperative Parathyroid Hormone Monitoring in Dogs with Hyperparathyroidism

Intraoperative Parathyroid Hormone Concentration to Confirm Removal of Hypersecretory Parathyroid Tissue and Time to Postoperative Normocalcaemia in Nine Dogs with Primary Hyperparathyroidism

K.J. Graham, M. Wilkinson, J. Culvenor, N.K. Dhand, and R.K. Churcher

Australian Veterinary Journal 2012;90:203-209.

Primary hyperparathyroidism is a relatively uncommon disease in dogs but must always be considered as a differential cause of hypercalcemia, particularly in an older, relatively asymptomatic dog with no evidence for malignancy (1-5). In primary hyperparathyroidism, parathyroid gland function is autonomous and nonresponsive to inhibition.  In approximately 90% of dogs, single parathyroid adenomas are responsible, but two adenomas, hyperplastic nodules or, rarely, carcinomas have been reported (2,6)

In human patients suffering from primary hyperparathyroidism, intraoperative parathyroid hormone (PTH) measurement is a highly sensitive and specific tool for determining successful removal of autonomously functioning parathyroid tissue (7-10). In this procedure, PTH is measured just prior to parathyroidectomy and at least 10 minutes after parathyroid tumor removal.  Since PTH has a plasma half life of less than 5 minutes (11), removal of a parathyroid tumor leads to a rapid fall in circulating PTH concentrations within minutes. The criterion for a positive test result varies between studies, but is generally accepted that > 50% decrease in PTH values indicates successful parathyroid tumor removal (7-10). A recent prospective veterinary study of 12 dogs demonstrated a greater than 50% reduction in parathyroidectomy PTH in all dogs, confirming correct removal of the hypersecretory gland (12).

The aims of this study by Graham et al (13) were to determine if serum PTH concentrations would decrease after successful parathyroidectomy and whether manipulation or dissection of the target gland would cause a transient increase in PTH, given its rapid half-life.

Objective of Study — To determine whether the intraoperative parathyroid hormone concentration (PTH) during parathyroidectomy can be used to indicate a cure in dogs with primary hyperparathyroidism. A secondary objective was to determine the time taken for the postoperative serum calcium concentration to normalize.

Design — Retrospective study (2005–2010) from a private referral hospital in Sydney, New South Wales, Australia.

Procedure — Nine client-owned dogs underwent surgical parathyroidectomy for naturally occurring primary hyperparathyroidism. The first PTH sample was taken immediately after induction of anesthesia and prior to manipulation of parathyroid tissue.  A second sample was collected as the abnormal parathyroid gland was being manipulated or excised in 6 dogs. A final PTH sample was taken 20–30 minutes after completion of parathyroidectomy in all dogs.

The concentration of ionized calcium (iCa) was measured at various time points postoperatively until it normalized, then stabilized or decreased below reference ranges. Statistical analysis compared the mean pre-, intra- and post-parathyroidectomy PTH concentration and the average rate of decline of iCa concentration postoperative.

Assays—Blood for PTH measurement was collected from the jugular vein and placed into plain tubes on ice for 30 minutes, centrifuged at 2500g and the serum transferred to a plain tube for storage at 4°C until assay. The serum specimens were assayed for PTH within 2 hours of collection, and results were available by the afternoon of surgery.

Intact serum PTH was assayed using an in-house, quick chemiluminescent enzyme immunometric assay, which is a modification of the Immulite PTH assay (Immulite Turbo: Siemens Medical Solutions Diagnostics).

Results – Serum PTH concentrations fell significantly when measured before and shortly after parathyroidectomy from mean pre-PTH value of 168.51 pg/mL to mean post-parathyroidectomy value of 29.20 pg/mL (Fig. 1). Intraoperative manipulation of the parathyroid tumor resulted in a significant increase in the mean PTH value to 279.78 pg/mL (Fig. 1). The average rate of decline of iCa concentration to within the reference range (1.12-1.40 mmol/L) occurred after 24 hours postoperatively.

Figure 1: Mean PTH concentration before surgery, at time of manipulation of the parathyroid tumor, and 20 min after parathyroidectomy.

Conclusions – Intraoperative measurements of PTH can be used clinically to determine cure of primary hyperparathyroidism. Parathyroid hormone increases significantly during parathyroid gland manipulation. Plasma iCa concentration returns to within the reference range on average 24 hours after successful parathyroidectomy. Not all dogs require vitamin D or calcium supplementation postoperatively.

My Bottom Line:

In this study (13), the investigators were able to document that use of intraoperative PTH in dogs undergoing parathyroidectomy for primary hyperparathyroidism can be a very powerful technique to determine successful surgical removal of the parathyroid tumor and predict outcome. Following parathyroid tumor removal, serum PTH fell dramatically when remeasured at 20-30 minutes postoperatively (see Figure 1). This agrees with another study performed in dogs in which serum PTH fell by >50% when rechecked 30-45 minutes after excision of the diseased parathyroid gland (12).

The finding that PTH concentrations can rise dramatically after manipulation of the abnormal parathyroid tissue highlights the importance of waiting at least 20 minutes to collect the final PTH sample after adenoma removal. This interval ensures that circulating PTH has had enough time to fall to it nadir level before collection.  If collected too soon, the PTH may still be too high, leading one to believe that the surgery was not successful.

Is intraoperative PTH testing practical?
The cost and availability of PTH assays is a major limiting factor for use of intra-operative PTH testing in dogs. Very few veterinary practices, even large speciality hospitals, will have access for the dedicated lab equipment needed to perform these assays. A nearby human facility was used in this case series reported by Graham (13), whereas the only other veterinary case series (12) performed quick parathyroid testing with a in-house, dedicated machine.

And that brings up the biggest down-side to this method —is it feasible to have the results of PTH testing back during the surgical procedure so that we know that all of the involved parathyroid tissue has been removed hyperfunctioning gland prior to closing?  If the PTH samples must be sent out to an outside lab for analysis, that typically will take a few days to receive the PTH results. Such a delay overrides or negates almost all of the advantages of this diagnostic technique.

Remember, as shown in this present study (13), we can judge the success of the operation on the basis of serial serum ionized calcium concentrations, which normalize by 24 hours after successful surgery. We do not need a serum PTH measurement to tell us that operation for hyperparathyroidism has been successful, at least not in most dogs with this disease.

References:

1. Berger B, Feldman EC. Primary hyperparathyroidism in dogs: 21 cases (1976-1986). J Am Vet Med Assoc 1987;191:350-356. 
2. Feldman EC, Hoar B, Pollard R, et al. Pretreatment clinical and laboratory findings in dogs with primary hyperparathyroidism: 210 cases (1987-2004). J Am Vet Med Assoc 2005;227:756-761. 
3. Gear RN, Neiger R, Skelly BJ, et al. Primary hyperparathyroidism in 29 dogs: diagnosis, treatment, outcome and associated renal failure. J Small Anim Pract 2005;46:10-16.  
4. Skelly BJ. Hyperparathyroidism In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Quedgeley, Gloucester: British Small Animal Veterinary Association, 2012;43-55.
5. Jores K, Kessler M. Primary hyperparathyroidism in the dog. Diagnosis, therapy and postoperative management in 19 dogs. Tierarztliche Praxis Ausgabe K, Kleintiere/Heimtiere 2011;39:389-396.
6. Sawyer ES, Northrup NC, Schmiedt CW, et al. Outcome of 19 dogs with parathyroid carcinoma after surgical excision. Vet Comp Oncol 2012;10:57-64. 
7. Irvin GL, 3rd, Solorzano CC, Carneiro DM. Quick intraoperative parathyroid hormone assay: surgical adjunct to allow limited parathyroidectomy, improve success rate, and predict outcome. World J Surg 2004;28:1287-1292. 
8. Sharma J, Milas M, Berber E, et al. Value of intraoperative parathyroid hormone monitoring. Ann Surg Oncol 2008;15:493-498. 
9. Richards ML, Thompson GB, Farley DR, et al. An optimal algorithm for intraoperative parathyroid hormone monitoring. Arch Surg 2011;146:280-285. 
10. Carneiro-Pla D. Contemporary and practical uses of intraoperative parathyroid hormone monitoring. Endocr Pract 2011;17 Suppl 1:44-53. 
11. Bieglmayer C, Prager G, Niederle B. Kinetic analyses of parathyroid hormone clearance as measured by three rapid immunoassays during parathyroidectomy. Clin Chem 2002;48:1731-1738.
12. Ham K, Greenfield CL, Barger A, et al. Validation of a rapid parathyroid hormone assay and intraoperative measurement of parathyroid hormone in dogs with benign naturally occurring primary hyperparathyroidism. Vet Surg 2009;38:122-132.  
13. Graham KJ, Wilkinson M, Culvenor J, et al. Intraoperative parathyroid hormone concentration to confirm removal of hypersecretory parathyroid tissue and time to postoperative normocalcaemia in nine dogs with primary hyperparathyroidism. Aust Vet J 2012;90:203-209.