By David Church, Deputy Principal and Acting Vice Principal (Clinical Affairs)

Hyperadrenocorticism (Cushing’s syndrome) is one of the most common endocrine diseases in dogs attending first-opinion veterinary practices. An RVC VetCompass study¹, based on data from 193,814 dogs attending 110 clinics, found an incidence of 0.28% in UK dogs.

Affected dogs’ adrenal glands produce too much cortisol due to either a pituitary tumour (pituitary-dependent hyperadrenocorticism) or a tumour in the adrenal gland itself. Pituitary-dependent hyperadrenocorticism (PDH) is much more common than the latter. 

Although the underlying cause of PDH in dogs is typically an adrenocorticotropic hormone (ACTH) producing tumour of the pituitary gland, treatment options for PDH have traditionally focused on the management of the resulting corticosteroid excess, using medications such as trilostane.

Therapy for PDH targeting the pituitary tumour itself involves either surgical excision of the pituitary gland and associated tumour (hypophysectomy) or radiation therapy. Unfortunately, although radiation therapy has been shown to reduce the size of the pituitary mass, it has been well documented that it does not reliably or effectively reduce excessive ACTH secretion and thus is not really a suitable treatment option for pituitary-dependent Cushing’s syndrome.

Following on from the success of the RVC's feline hypophysectomy programme for the management of feline hypersomatotrophism, our neurosurgical hypophysectomy specialists, headed up by Joe Fenn, have been adapting their techniques to manage pituitary-dependent Cushing’s syndrome via hypophysectomy. An increasing number of dogs have undergone this treatment and almost without fail have shown a pleasing return to normality with effectively complete resolution of the clinical signs referable to Cushing’s syndrome.

While hypophysectomy is addressing the core of the problem – removing the offending functional endocrine pituitary tumour – the costs and risks associated with ‘brain surgery’ are not for everyone. Another VetCompass study² showed that over 80% of owners were not satisfied with medical management of their dog with pituitary-dependent Cushing’s, that less than 15% thought the response with trilostane treatment was good and that over 90% of dogs with Cushing’s treated with trilostane in UK general practices were euthanised within 15 months of diagnosis because of “poor responses to treatment”.

Clearly medical management with trilostane is not working for a substantial proportion of people and because of costs, risks and general “fear of brain surgery”, hypophysectomy is not for everybody either.

What can be done?

In 2020 is there another realistic option for managing pituitary-dependent Cushing’s syndrome?

The answer is a resounding YES! Perhaps surprisingly the answer is based upon another surgical rather than medical option – bilateral adrenalectomy! In other words, ask our soft-tissue surgery team to remove the source of the excess and uncontrolled over-production of cortisol – the same principle that underpins the use of trilostane, but just using a surgical rather than a medical approach to achieve the desired outcome.

Our soft-tissue surgical team here at the QMHA have considerable experience in carrying out bilateral adrenalectomies to manage pituitary-dependent Cushing’s syndrome and then managing the patients as Addisonians.

In terms of surgical and peri-operative complications, bilateral adrenalectomies are no more problematic than any other flank celiotomy. Patients are managed as we would any Addisonian with appropriate doses of cortisone (yes not prednisolone) and non-manufacturer-recommended doses of DOCP.

I wonder if I might ask you all a simple question? If your own dog had to have an adrenal endocrinopathy – pheochromocytoma, pituitary-dependent Cushing’s or Addison’s disease – which would you select?

I am sure the vast majority of you would select Addison’s disease. If that is the case, could I suggest that with the next pituitary-dependent Cushing’s dog you see, could you at least consider managing it with bilateral adrenalectomy and saving yourself and the owner a lot of expense and heartbreak.

References

1. Schofield, I., Brodbelt, DC., Wilson, ARL., Niessen, S., Church, D., O'Neill, D. (2019) ‘Survival analysis of 219 dogs with hyperadrenocorticism attending primary care practice in England’. Veterinary Record
2. O'Neill, D. G., Scudder, C., Faire, J. M., Church, D. B., McGreevy, P. D., Thomson, P. C. and Brodbelt, D. C. (2016), ‘Epidemiology of hyperadrenocorticism among 210,824 dogs attending primary-care veterinary practices in the UK from 2009 to 2014’. J Small Anim Pract, 57: 365–373.