Page 1587 - Clinical Small Animal Internal Medicine

172 Metabolic Bone Diseases 1525

In humans, rickets and osteomalacia are described in of the reported cases of rickets in the literature, puppies
VetBooks.ir patients with gastrointestinal malabsorption disorders, were fed a diet of milk and meat. Such a diet would likely
due to failure to absorb fat‐soluble vitamins such as
meet the calcium and phosphorus requirements for the
vitamin D, and reduced absorption of calcium. Rickets
tion of milk is low.
has been described in a 17‐week‐old male border collie animals, but not vitamin D, as the vitamin D concentra­
with extrahepatic biliary atresia. A case of rickets has occurred in a 10‐week‐old
Aluminium toxicity from chronic antacid administra­ Shetland sheepdog on a commercial renal failure diet.
tion or long‐term total parenteral nutrition may also Such diets are designed to be low in phosphorus and
cause rickets and osteomalacia in humans. protein in order to alleviate some of the clinical and bio­
Osteomalacia may occur in combination with FOD in chemical changes associated with the disease. However,
dogs and cats with chronic kidney disase. Hyperphos­ the level of phosphorus in the diet fed to this young
phatemia results in increased plasma FGF23 concentra­ dog was inadequate for a growing animal, leading to
tions, leading to inhibition of the renal 1‐alpha‐hydroxylase phosphorus deficiency and rickets. Similarly, osteomala­
enzyme, causing decreased production of 1,25(OH) 2 D 3 . cia has been reported in an adult dog with food allergies
This combination of osteomalacia and FOD is often fed an unbalanced elimination ration.
termed renal osteodystrophy. As mentioned earlier, Affected animals present with lameness, reluctance to
while bone changes do occur in adult animals with walk, and a failure to grow and gain weight. Animals may
chronic kidney disease, the changes seldom result in have angular limb deformities, particularly affecting the
clinical signs. forelimbs. Rickets most commonly affects rapidly grow­
Vitamin D also has an important role in the immune ing physes, such as the distal radius, proximal tibia, distal
system, and has been associated with many different dis­ femur, and proximal humerus. The metaphyses of long
eases in both humans and animals. Low serum 25OHD bones, particularly the distal radius, may be swollen.
concentrations in dogs have been associated with Animals may have swollen costochondral junctions,
immune‐mediated disorders, various types of cancer, known as the rachitic rosary. Affected animals may have
acute pancreatitis, progression of leishmania, chronic pathologic fractures, and delayed eruption of teeth and
enteropathy, chronic valvular heart disease, and poor enamel hypoplasia may also be seen. In animals with
outcome in congestive heart failure, while in cats, low severe hypocalcemia, seizures may be the presenting
serum 25OHD has been associated with inflammatory clinical sign.
bowel disease, intestinal small cell lymphoma, and myco­ Osteomalacia is reported rarely in dogs, and this may
bacteriosis. However, care should be taken not to overin­ partly be due to the subtlety of the clinical signs. The
terpret the role of vitamin D in these diseases. Correlation most common clinical sign of osteomalacia in humans is
is not causation, and randomized clinical trials are bone pain, and in older dogs this may easily be mistaken
required to determine the significance of vitamin D in as reluctance to move due to chronic degenerative joint
the pathogenesis of different diseases and whether disease and not investigated further.
changes in serum 25OHD are primary or occur second­
ary to the disease.
Diagnosis
Biochemistry
Signalment
Animals with rickets due to vitamin D deficiency will
Rickets occurs in young animals and cases of rickets in have decreased or low normal serum calcium concentra­
the literature have been reported in 10–14‐week‐old pup­ tion, hypophosphatemia, increased serum alkaline
pies and kittens. Nutritional rickets has been reported phosphatase activity, and increased plasma PTH concen­
most commonly in greyhound litters, presumably because tration. Serum vitamin D concentrations depend on the
these animals are more likely to be fed unusual diets. inciting cause of the rickets. In vitamin D deficiency
Rickets is extremely rare in cats, and naturally occur­ rickets, usually both serum 25OHD and 1,25(OH) 2 D 3
ring nutritional rickets has not been reported in the concentrations are decreased. However, confusingly in
literature. However, rickets has been induced experi­ some cases, the increase in PTH as a result of hypocalce­
mentally in both cats and dogs fed vitamin D‐deficient mia leads to increased activity of the renal 1‐alpha‐
diets. hydroxylase and normal to increased serum 1,25(OH) 2 D 3
concentrations. Despite this, low serum 25OHD indi­
cates there is insufficient vitamin D being obtained
History and Clinical Signs
from the diet.
As with nutritional FOD, animals with rickets usually In phosphorus deficiency rickets, animals have severe
have a history of an unusual postweaning ration. In two hypophosphatemia but serum calcium and 25OHD