Page 36 - VetCPD Jnl Volume 7, Issue 4

Diagnosis and treatment
The remainder of this article aims to address diagnosis and treatment by answering some of the most common questions that are posed by clinicians.
Frequently Asked Questions:
Is the sodium:potassium ratio considered useful in diagnosing hypoadrenocorticism?
Typically, hypoadrenocorticism will lead to hyponatraemia and hyperkalaemia.
VETcpd - Internal Medicine
Table 1: A summary of clinical and clinico-pathological findings in dogs with hypoadrenocorticism
CLINICAL SIGNS
CLINICO-PATHOLOGICAL FINDINGS
Common
Lethargy Anorexia Vomiting Diarrhoea Weakness Collapse Abdominal pain Dehydration Nausea
Muscle weakness
No stress leucogram Non-regenerative anaemia Hypoalbuminaemia Hypercalcaemia Hyponatraemia Hyperkalaemia
Azotaemia USG <1.030
Neutropenia Lymphocytosis Eosinophilia Hypoglycaemia Hypocholesterolaemia USG <1.015
ers
A low Na:K ratio is often considered to
be consistent with hypoadrenocorticism
and historically ratios <27:1 have been
used to suggest a diagnosis.Whilst this
has a relatively high specificity (94%),
the sensitivity is only 70% (Seth et al.
2011). As the ratio decreases further the
specificity increases.Abnormalities in one
electrolyte due to other causes can alter
the ratio, therefore it is more important
to look at the electrolyte concentrations
rather than the ratio (Neilsen et al. 2008). Polyuria/polydipsia Importantly, cases of suspected isolated Hypovolaemia hypocortisolaemia should have a normal Cardiac arrhythmia
Less common
Weight loss Regurgitation Shaking/trembling Seizures
cause a low Na:K ratio? Hypotension Subscrib
Na:K ratio. Bradycardia
Can anything else Mental depression
Several conditions can mimic
hypoadrenocorticism with regards Only
to the abnormal electrolyte concentrations and this is often termed ‘pseudohypoadrenocorticism’.These include chylothorax, periparturient disease and gastrointestinal diseases such as Salmonellosis and Trichuriasis.
What do I do if a dog has already had steroids prior to an ACTH stimulation test?
Clinicians are frequently presented with a situation where a patient with suspected hypoadrenocorticism has been treated with corticosteroid of some form (either systemic or topical). In the case of the patient having received a single injection of dexamethasone more than a few hours previously, and assuming the clinical condition of the patient allows it, it would be considered reasonable to administer symptomatic treatment until an ACTH stimulation test can be performed, ideally at least 36 hours later.A single dose of dexamethasone could cause suppression of the HPA axis; however, it is still generally possible to differentiate a patient with
a low cortisol concentration due to a single dexamethasone injection from the "flat-lined" response seen in a patient with primary hypoadrenocorticism.A previous study shows that a single intravenous
injection of dexamethasone, of greater is history of longer-acting corticosteroid than or equal to 0.1mg/kg, can alter the use. It is also worth bearing in mind results of the ACTH stimulation for at least that some corticosteroids will cross- two days; however, the suppressive effect react with the cortisol assay, therefore is dose dependent and not apparent after increasing the measured cortisol in the seven days (when treated with 1mg/kg ACTH test result, thus allowing cases of dexamethasone) (Kemppainen et al. 1989). hypoadrenocorticism to be ‘missed’ (see It is important to remember that any Table 2). Dexamethasone will not cause corticosteroid, even those contained in
topical medications, can suppress the HPA axis. Ideally, if a patient has received a long duration of steroid treatment, then one would wait at least three weeks before performing an ACTH stimulation test. One study demonstrated complete HPA axis recovery two weeks after oral administration of an anti-inflammatory regimen of prednisone given daily for five weeks (Moore & Hoenig 1992). Another study demonstrated that a single intramuscular injection of triamcinolone can cause suppression of adrenocortical function in some dogs for up to four weeks (Kemppainen et al. 1982). Therefore, whilst the exact delay that is necessary is debatable, waiting a period of at least 3-4 weeks is assumed to be adequate to decrease false-negative or false positive results; however, this length of time may need to be extended if there
this cross-reaction, therefore in truly critically unwell cases an injection of dexamethasone could be administered concurrently whilst performing an ACTH stimulation test.
VETcpd - Vol 7 Issue 4 - Page 33
VETcpd - Vol 7 Issue 4 - Page 33
Table 2: Immunoreactive and suppressive corticosteroids
IMMUNOREACTIVE (CROSS-REACTS WITH CORTISOL ASSAY)
SUPPRESSION OF HPA AXIS
Prednisolone Prednisone Hydrocortisone Triamcinolone
Prednisolone Prednisone Methyl-prednisolone Hydrocortisone Dexamethasone Triamcinolone