Page 119 - Clinical Small Animal Internal Medicine

11 Hypoadrenocorticism in Dogs and Cats 87

“Stressful” situations include physiologic and Epidemiology
VetBooks.ir emotional stress, such as when a dog goes to the hypoadrenocorticism. However, due to its vague clinical
Atypical hypoadrenocorticism is an uncommon form of
veterinary clinic for electrolyte rechecks, when new
signs and lack of electrolyte abnormalities on serum bio-
visitors are in the household, when the dog goes hunt-
ing (if applicable), and when the dog has a concurrent chemistry, it is likely underdiagnosed.
illness. The increased dose is usually started the
morning before the stress begins, and continued for a Signalment
day or two following the end of the stressful event. The signalment for atypical HOAC is similar to that of
Astute clients are usually able to identify when their typical HOAC. Young to middle‐aged dogs are predis-
dog needs additional prednisone, and adjust the dose posed, as are poodles, West Highland white terriers, Great
appropriately. However, some clients need frequent Danes, and NSDTRs. However, any breed of any age may
reminders, particularly when they present for electro- be affected.
lyte evaluation.
History and Clinical Signs
Historical findings and clinical signs associated with
Prognosis
atypical HOAC are similar to those in typical HOAC.
With appropriate treatment and monitoring, the prog- Addisonian crisis does not usually occur with atypical
nosis for dogs with naturally occurring hypoadreno- HOAC, partially because hyperkalemia and hypona-
corticism is excellent. Dogs enjoy a good quality of tremia are not present. Nonspecific signs such as weight
life, and may participate in normal activities, as long loss, lethargy, and anorexia predominate, while gastroin-
as they are provided with additional prednisone as testinal signs such as vomiting and diarrhea are also
needed. Consistent medication and patient monitor- common. Atypical HOAC should always be considered
ing must be stressed to owners, as poor medication in dogs with chronic GI signs, especially if they are more
compliance or prolonging the treatment interval for common when the dog is stressed (such as “stress coli-
DOCP, without veterinary approval, may lead to tis”). Seizures secondary to hypoglycemia and megae-
Addisonian crisis. sophagus are uncommon, but atypical HOAC should
remain on the rule‐out list for dogs with megaesophagus
and hypoglycemia, even if they have normal electrolyte
Atypical Hypoadrenocorticism
concentrations. PU/PD may also be reported in dogs
Etiology/Pathophysiology with atypical HOAC.
Atypical hypoadrenocorticism refers to hypoadreno-
corticism with clinical signs attributable to cortisol Diagnosis
deficiency only; electrolyte concentrations are within Dogs with atypical HOAC may have many of the same
reference range. At this time, the etiology is unknown. clinicopathologic abnormalities as dogs with typical
Individual cases may result from different etiologies. HOAC, except for hyperkalemia, hyponatremia, and
In some cases, partial immune‐mediated destruction hypochloremia. Although mild to moderate azotemia is
of the adrenal cortex occurs, sparing the zona glomer- possible, it is less common and less severe than in typical
ulosa and aldosterone synthesis. Occasionally, this is HOAC. Anemia and hypoalbuminemia are more com-
an early manifestation of “typical” hypoadrenocorti- mon in dogs with isolated cortisol deficiency, likely
cism, and the glomerulosa is eventually destroyed, because typical Addisonians are more hemoconcen-
leading to concurrent electrolyte abnormalities. In trated (hypovolemic) than atypical Addisonians.
other cases, dogs may actually be aldosterone defi- Hypocholesterolemia is also common, and hypoglyce-
cient but able to compensate and maintain normal mia can also occur and result in seizures.
electrolyte concentrations. The compensatory mecha- Definitive diagnosis of atypical hypoadrenocorticism
nisms are unclear, but aldosterone deficiency has relies upon the ACTH stimulation test, and is interpreted
been documented in patients with normal electrolyte the same way as with typical hypoadrenocorticism. A
concentrations. more economical way to rule out atypical HOAC is to
Secondary hypoadrenocorticism, due to ACTH defi- measure the baseline cortisol; patients with cortisol
ciency, results in signs of cortisol deficiency without >2-3 μg/dL do not have the disease. However, if the base-
electrolyte abnormalities, as well. However, secondary line cortisol is <2 μg/dL, an ACTH stimulation test is
HOAC can be identified by low to nonexistent ACTH necessary for diagnosis. Although atypical HOAC is
concentrations. Dogs with atypical HOAC have nor- uncommon, it is easily treated and has a good prognosis.
mally functioning pituitary glands, and usually increased Thus, testing is indicated in patients with unexplained
ACTH concentrations. GI signs, lethargy, and weight loss.