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VETcpd - Internal Medicine
Is there any value in just evaluating basal cortisol? When do I need to be suspicious of hypoadrenocorticism? Basal cortisol may be used as a ‘screening test’ to exclude hypoadrenocorticism, with concentrations >55nmol/L considered reliable for excluding the disease (Bovens et al. 2014; Gold et al. 2016). Whilst this approach is considered useful for cases with a more chronic history, if patients are unstable at presentation or the clinical suspicion is high, an ACTH stimulation test should be performed so as not to delay diagnosis and treatment.
assessment of serum potassium and blood pressure at the time of sample collection.
In an unpublished series of cases examining ACTH-stimulated aldosterone in dogs with suspected isolated hypocortisolaemia, the majority of
cases did not appear to have functional aldosterone reserve. In these cases with a lack of aldosterone reserve the conclusion is that these patients have conventional hypoadrenocorticism despite normal electrolytes (Thompson 2019).
1-3 months for at least the first 12 months’ following diagnosis. Owners should also be educated about monitoring for clinical signs of mineralocorticoid deficiency. Most dogs that progress to complete adrenal failure will do so within one year of diagnosis (Lifton et al. 1996;Thompson et al. 2007). Discussion with a medicine specialist may be warranted in complicated cases.
My ACTH stimulation test suggests hypoadrenocorticism, should I measure endogenous ACTH? Are there any other tests I should consider? Following on from the previous
Dogs with presumed primary isolated hypocortisolaemia will, at least
initially, only require glucocorticoid supplementation. Long-term follow up of hypoadrenocorticism cases with normal electrolytes have demonstrated that a small proportion of dogs develop electrolyte abnormalities but most dogs remain glucocorticoid deficient only. Although only small groups of dogs have
questions, if sodium and potassium concentrations remain normal then the patient may not require mineralocorticoid supplementation. Measurement of endogenous ACTH may help discriminate between primary and secondary hypoadrenocorticism. Dogs with primary hypoadrenocorticism would be expected
What is isolated hypocortisolaemia/
atypical Addison’s disease, and when
do I need to be worried about it?
Approximately 10-20% of cases of
hypoadrenocorticism may have normal
serum electrolyte concentrations
(Thompson et al. 2007; Baumstark et al.
2014).Whilst historically these cases were been evaluated, only 11%-14% of cases to have ACTH concentrations above referred to as ‘atypical hypoadrenocorti- of isolated hypocortisolaemia developed reference range, whereas dogs with
cism’ more recent literature suggests electrolyte abnormalities between secondary hypoadrenocorticism will have that this is an inappropriate use of the 2 – 51 months after initial diagnosis. very low concentrations (summarised in term (Baumstark et al. 2014) and the (Thompson et al. 2007;Wakayama Table 3).The relevance of this is two-fold. term 'isolated hypocortisolaemia' may et al. 2017). It should be noted that Firstly, if secondary hypoadrenocorticism
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be preferable.This condition may occur aldosterone was not measured in most is suspected then this may encourage the
secondary to gradual loss of adrenocortical of these cases. It is possible that these clinician to investigate for intracranial tissue, where the loss of the glucocorticoid patients are able to maintain normal disease. Secondly, the assumption is that
secreting portion precedes loss of the mineralocorticoid secreting portion,
or perhaps more commonly there is a selective loss of cortisol production.A more appropriate definition is perhaps ‘hypocortisolaemia in the presence of normo-aldosteronaemia’. It has generally been assumed that these cases are deficient in cortisol but have preserved mineralo- corticoid function. However, this is based on the assumption that normal electro- lytes can be used as a surrogate marker
of the presence of normal aldosterone concentrations which we know may not be the case as there are other mediators of potassium concentration.
Like cortisol, aldosterone can be
measured on separated serum samples.
A high basal aldosterone can exclude hypoaldosteronaemia; however, a stimulation test is necessary to make
a diagnosis.Although only a minor stimulant of aldosterone,ACTH can be used to stimulate aldosterone release (Baumstark et al. 2014). Pre and post ACTH aldosterone concentrations have been shown to be lower in dogs with hypoadrenocorticism than in healthy
dogs (Muller et al. 2007).The results should be interpreted in conjunction with
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• Mineralocorticoid activity aldosterone is unmeasurable then it will Only
of prednisolone confirm the need for mineralocorticoid • Impaired sensitivity of the supplementation in many cases and
electrolyte concentrations in the face of dogs with secondary hypoadrenocorticism hypoaldosteronaemia due to: will not require mineralocorticoid
• Inherent compensation mechanisms supplementation.
which act to regulate potassium An ACTH-stimulated aldosterone test
to a degree (without aldosterone) could be considered as an initial alterna-
• Inherent day-to-day variability tive to measuring endogenous ACTH. If
aldosterone receptor
• The absence of genuine
physiological ‘stress’
Some clinicians may choose to supplement with mineralocorticoid
in isolated hypocortisolaemia without documenting hypoaldosteronism.Whilst this gives the advantage of hopefully avoiding potentially fatal decompensation, it represents a financial cost to owners
and determining accurate dosing of desoxycorticosterone pivalate (DOCP) can be difficult.
Although an aldosterone stimulation
test at diagnosis may provide additional information, it is not considered mandatory. In patients with pre and
post ACTH cortisol of <27nmol/L and normal electrolytes, a reasonable approach would be to monitor electrolytes every
exclude secondary hypoadrenocorticism. However, this will not aid differentiation of primary atypical/isolated hypocortisol- aemia vs. secondary disease.
Which fluids should I use in
an acutely unwell patient?
Classically, clinicians might think they should use potassium-free solutions such as 0.9% saline. However, balanced potassium- containing fluids (such as Hartmann’s or Plasmalyte) are not necessarily contrain- dicated as they contain only very small amounts of potassium. In fact, care should be taken in these cases not to increase sodium too rapidly.
Should I use dexamethasone or hydrocortisone for acute management? Either dexamethasone or hydrocortisone can be used in the acute management of hypoadrenocortical crises (see Table 4).