Page 146 - Clinical Small Animal Internal Medicine

114 Section 2 Endocrine Disease

adrenal insufficiency reported four with concurrent performed because of continued lethargy despite
VetBooks.ir hypothyroidism, one dog with concurrent IDDM and adequate mineralocorticoid replacement therapy, persis­
tent hyponatremia, hypercholesterolemia, dermatologic
one dog with concurrent primary gonadal hypoplasia.
A single case of type 2 APS has been described in a
In cases of combined DM and hypothyroidism, diabetes
middle‐aged female dog presenting in a hypothyroid disease, bradycardia, obesity, and heat‐seeking behavior.
crisis; treatment of the hypothyroid state resulted in mellitus insulin resistance is usually the reason for
precipitation of the hypoadrenocorticism. The presence thyroid testing.
of serum autoantibodies to thyroid and adrenal tissue
was observed in this dog as evidence of APS type 2.
Diagnosis and Prognosis

History and Clinical Signs In two studies, dogs with concurrent diabetes and hypo­
thyroidism showed significantly lower serum sodium
Most of the dogs in reported studies were diagnosed with concentration and had significantly higher fasting serum
hypoadrenocorticism initially and the mean age of onset cholesterol compared with nonhypothyroid diabetic
of the disease was in young adulthood. Dogs are usually dogs; similarly, dogs with hypoadrenocorticism com­
diagnosed with a second endocrinopathy approximately bined with hypothyroidism exhibited significantly lower
one year after the first endocrinopathy. sodium and higher serum cholesterol than dogs with
A familial tendency was observed in one study where hypoadrenocorticism alone. These two chemistry abnor­
two dogs were mother and daughter and one dog had a malities are highly suggestive of hypothyroidism in a dog
sibling with hypoadrenocorticism. Hypoadrenocorticism with otherwise well‐regulated hypoadrenocorticism or
is inherited in several breeds, including standard poodles, in a poorly regulated diabetic dog. Severe hyponatremia
West Highland white terriers, Nova Scotia duck tolling (<120 meq/L) is a sign of Schmidt syndrome in humans.
retrievers, Portuguese water dogs, and Leonbergers; how­ Thyroid testing should be performed in diabetics dogs
ever, there may be different DLA haplotypes depending that exhibit poor glucose regulation, persistent hypona­
on breed. There is a distinct breed predisposition for tremia and hypercholesterolemia, obesity or weight gain,
primary hypothyroidism with golden retrievers, lethargy, dermatologic disease, and regurgitation.
Doberman pinschers, Irish setters, miniature schnauzers, Resting serum cortisol concentration is often subnormal
dachshunds, cocker spaniels, and beagles. Diabetes (<2 μg/dL) in dogs that suffer from APS 2 that manifests as
mellitus (type 1a), which has an autoimmune basis, is seen hypoadrenocorticism and all will show inadequate
with increased frequency in Samoyeds, Tibetan terriers, response to adrenocorticotropic hormone (ACTH) stimu­
Australian terriers, keeshonds and several other breeds. In lation. Endogenous ACTH levels should be increased due
fact, one study showed that the DLA‐DRB1*009/DQA1*/ to primary adrenal insufficiency and loss of negative feed­
DQB1*008 haplotype was associated with DM in certain back to the pituitary gland. One reported case of Schmidt
breeds (Samoyed, Tibetan, and cairn terriers) and that the syndrome (APS 2) had evidence of lymphocytic adenohy­
DLA‐DQA1*001 allele is also associated with hypothy­ pophysitis in addition to adrenalitis and thyroid gland
roidism in dogs, suggesting a common susceptibility allele atrophy; immune‐mediated pituitary disorders have been
for canine immune‐mediated endocrinopathies. reported in humans as well. Mean basal thyroxine (T4)
A decreasing insulin requirement is often the earliest and free T4 levels are usually low to low normal and
sign of adrenal insufficiency in a patient with type 1 endogenous thyroid‐stimulating hormone (TSH) is usu­
diabetes mellitus secondary to APS in human beings. ally elevated in dogs with multiple endocrinopathies
In contrast, dogs with concurrent hypothyroidism resulting from APS.
and IDDM often have increasing insulin requirements;
hypothyroidism may cause insulin resistance resulting
from lipid abnormalities or other factors. Therapy
The most common presenting complaints for hypoad­
renocorticism as the initial diagnosis include lethargy, Treatment of multiple endocrinopathies consists of
collapse, vomiting, weight loss, weakness, ataxia, anorexia, specific hormone replacement. For dogs with hypoad­
bradycardia, megaesophagus, and diarrhea. Clinico­ renocorticism, treatment with fludrocortisone (0.018 mg/
pathologic features include hyponatremia, hypercholes­ kg PO q24h) or deoxycorticosterone pivalate (DOCP)
terolemia, hyperkalemia, hypochloremia, azotemia, (1 mg/kg IM monthly) should be initiated first, followed
hypocalcemia, and hypercalcemia. by levothyroxine therapy (22 μg/kg once or twice daily
In dogs diagnosed with hypoadrenocorticism as PO). One should be aware that aggressive levothyroxine
the initial endocrinopathy, thyroid evaluation is often therapy might precipitate a life‐threatening adrenal crisis