Bichons, Calcium Oxalate Stones and Hyperparathyroidism
(Is there a connection?)
Anne Jones RN, BSNE

Is there a relationship in Bichons with calcium oxalate stones to the health of the parathyroid gland?  This is a question that I have asked for several years.  The answers were generally a shrug, a maybe or just "I don't know", none of which satisfied me.  I had good reasons for asking the question of the several veterinarians that I approached.  We will look at the facts but first an anatomy lesson may be in order.  Most people don't even know there are such things as parathyroid glands, much less any details about what they do.

The four parathyroid glands are located on either side of the thyroid gland, in the neck, but there can be more or fewer glands and there can be a gland at some distance from the thyroid gland.  Or at least that is the case in humans.  They are tiny but have very important functions, primarily in regard to how calcium behaves in the body.  Following thyroidectomy, blood calcium levels are monitored because of the dangers within the body if all parathyroid tissue is removed along with the thyroid gland. 

The parathyroids excrete a hormone called parathyroid hormone (PTH).  98% of body calcium is found in skeletal tissue (bone) and calcium utilization in the body is controlled by PTH.  Without going into more detail that you can use, the balance between serum calcium and PTH is also affected by Vitamin D, another hormone that is influenced by exposure to sunlight and by dietary consumption.  This may already be more information than you wanted but it shows in yet another way the complexity of the body, human or canine, and its health.

This article will sometimes address what happens in humans because much of the written material on canine parathyroid disease uses known human data.  It is also influenced by my personal experience with hyperparathyroidism and subsequent surgery.  First we need to establish certain known facts, some of which are used to describe parathyroid function in humans as a way to illustrate possible connection to hyperparathyroidism in canines.  Until recently minimal research on canines had been published in connection with calcium oxalate stones.  Even a recent publication uses human disease for illustration.

FACTS:

•  Primary Hyperparathyroidism (PHPT) is usually caused by adenoma, a benign tumor, of a parathyroid gland.  Rarely caused by malignancy but neoplasia should be ruled out

• Mild to moderate hypercalcemia may cause no obvious clinical signs

•  In humans, 20% first become aware of PHPT when they develop kidney stones

• Calcium oxalate uroliths (stones) and/or calcium phosphate stones or a mixture of the two appear to have a strong relationship to hyperparathyroidism in dogs

• Calcium oxalate stones are found primarily in a half dozen breeds predisposed to calcium oxalate uroliths; they are Miniature Schnauzers,  Miniature Poodles, Lhasa Apsos, Yorkshire Terriers, Shih Tzus and Bichons Frises

• Keeshonden statistically have the highest occurrence of PHPT/hypercalcemia, according to the recent research study by Richard E. Goldstein DVM

• One earlier study of dogs with PHPT showed that 31% of them had uroliths

• PHPT predisposes dogs to bone resorption, causing softening of bone tissue (I lost two inches in height!).  In humans it appears that the bone hardens again once the problem is resolved (my bone density studies have shown this to be true in my own body)

• Diagnosis beyond signs of the disease (calcium urolith formation, bone softening, etc) is made by ultrasound, blood studies and x-rays

• High calcium in dogs may cause cancer of the kidneys, renal problems, Addisons, Vitamin D toxicity (Cushings is also found in some human patients)

• Clinical signs in dogs may include increased thirst and urination; weakness, lethargy, trembling, bladder or kidney stones - there may be none of the above in the early stages

• Treatment is by surgery to remove a gland with an adenoma but other options are by ethanol injection or heat ablation to destroy that gland

• Postoperative monitoring for clinical hypoglycemia must be intensive and must be maintained for several days to avoid even more serious issues relating to lack of blood calcium.  These dogs may be kept in hospital for 5-10 days. 

Dr. Richard Goldstein, Cornell University research scientist, has completed genome research funded by the Keeshond Club of America and AKC Canine Health Foundation, with positive results.  There is now a genetic test available in Keeshonden and sanctioned by OFA.  The following facts apply to Keeshonden but should be provided to you as a part of available information on PHPT:

• PHPT is hereditary in Keeshonden

•  Incomplete dominant

• In research, the specific gene mutation was present in 35 of 35 affected dogs but was also present in 11 of 144 unaffected dogs.   This indicates the presence of the gene and can be passed along to their offspring

• A dog with two affected alleles was not seen, possibly because two alleles would be lethal to the whelps

• In Keeshonden, affected dogs are older, averaging 10.5 years.  (We see stones at a younger age in Bichons)

What are the implications in regard to Bichons?  As a disclaimer, I have to admit I had already assumed hyperparathyroid disease could be the causative issue in our breed's high incidence of calcium oxalate stones.  That said, it appears BFCA may need to pursue further research into inheritance in our breed, with a focus on possible relationship of PHPT to calcium oxalate stones.  What you can do as a breeder or owner of a Bichon with calcium oxalate stones is to bring up the issue with your own veterinarian.  Feel free to share this article because it is based on known factual information in both humans and in canines. 

In summary, humans presenting with bladder/kidney stones, especially those with high calcium content, or humans with elevated blood calcium levels (which was my problem - I never had stones) should be tested for excessive levels of parathyroid hormone.  I mention this again because you may have a family member with similar history who needs to know this.  Dogs with calcium oxalate history (ancestry) should be tested and should not be used for breeding unless and until we have genetic testing that rules out PHPT and/or establishes inheritance patterns.  If these dogs are used, there should be great care taken to select as mates Bichons with NO history of calcium oxalate stones in their ancestry.  Surgery removes the affected parathyroid gland but does not change the genetic inheritance.  If we want to eliminate this costly and painful condition in our dogs, we need to address it sensibly and thoroughly.  This is a harsh statement and likely will not be what anyone wants to hear.  We have long known it is not the food we feed or the water they drink that causes Bichons to have bladder infections, crystals and stones with calcium content.   As with all genetic/heritable disease only positive action will eliminate it from our gene pool.

(Footnote: Joseph Bartges DVM, University of Tennessee, has a grant proposal prepared for study of uroliths in Bichons Frises and will likely request some funding from BFCA.  If this is approved, you may be asked to participate in the study.  To date he has seen no evidence of parathyroid disease in the breed but is aware of my questioning a possible relationship)

Resources:

http://www.akcchf.org/pdfs/whitepapers/CHFSummaryReport2007.pdf (see page 19)

"The ROCKet Science of Canine Urolithiasis", Cart A. Osborne DVM et al, The Veterinary Clinics of North America, Vol. 29, No. 1, Jan. 1999, pgs 146-147

"Dog Owners Veterinary Handbook", Carlson DVM and Giffin MD, pgs 239-240