Zycortal Symposium Proceedings

prednisolone (around 0.08 mg/kg daily) and perform the test one week later. If a flat lined response was obtained, then repeating of the stimulation test would be recommended one to two weeks later. The cross-reactivity of some exogenous steroid preparations with the cortisol assay (prednisolone and hydrocortisone) is as equally important to consider as the suppression of the HPA axis. It was clear that basal cortisol (>55nmol/l) was frequently being used as a rule out test for hypoadrenocorticism, in patients with non-specific chronic signs. In patients with a high index of suspicion for the disease, it is still recommended to proceed with an ACTH stimulation test, however for financial and practical reasons, basal cortisol should be considered in patients with signs such as chronic gastrointestinal signs. It was discussed whether or not basal cortisol should be included in routine biochemical panels as this may increase the diagnosis of atypical cases of Addison’s disease in practice. However it was decided that this may lead to incorrect diagnosis of the condition or lead to an increased number of ACTH stimulation tests being performed in patients unlikely to have to condition. Instead, it was decided that first opinion vets should be educated on the use of basal cortisol in patients with chronic gastrointestinal signs or chronic weight loss. 1. Normal electrolytes, low aldosterone. In these patients there would appear to be destruction of the zona glomerulosa as well as the fasciculata/reticularis. The electrolytes would appear to be normal due to compensatory mechanisms. 2. Normal electrolytes, normal aldosterone, no stimulation of aldosterone following ACTH stimulation. In these patients, it is speculated that only partial destruction of the zona glomerulosa exists. Ongoing destruction of the zona glomerulosa is possible and therefore the aldosterone could subsequently become low. 3. Normal electrolytes, normal aldosterone, stimulation of aldosterone following ACTH. This group represents the true “atypical” group, who appear to have destruction of the zona fasciculata/ reticularis only. It was agreed that the term “atypical” Addison’s disease should be used for the third group. The first group should be termed “typical primary hypoadrenocorticism with normal electrolytes” and group two “typical primary hypoadrenocorticism with normal electrolytes and partial aldosterone deficiency”. What is “atypical” Addison’s disease? This has been a controversial and extensively discussed subject in the past. It was recognised that there may be three subgroups of “atypical” Addison’s disease:

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