Cushing's disease, also known as hyperadrenocorticism, develops in dogs that produce excessive amounts of adrenal hormones, corticosteroids in particular. Corticosteroid overproduction occurs either as a result of the presence of pituitary or adrenal gland tumours (spontaneous Cushing's) or from over-administration of steroid medications (iatrogenic Cushing's). Cessation of steroidal treatments will reverse iatrogenic Cushing's; however, spontaneous Cushing's is much more difficult to treat. A dog suffering from spontaneous Cushing's may develop neurological complications such as seizures.
Spontaneous Cushing's cases result from tumours of either the pituitary gland or the adrenal gland. Pituitary tumours cause approximately 85 per cent of spontaneous Cushing's cases by overproducing the hormone that instructs the adrenal glands to manufacture cortisones. Adrenal gland tumours, which account for the remaining 15 per cent of spontaneous Cushing's cases, keep the adrenal glands in constant production of cortisones despite efforts by the pituitary gland to regulate the body's cortisone levels. In either circumstance, cortisol rises to abnormal levels in the body and triggers Cushing's symptoms.
Spontaneous Cushing's/Seizures Connection
Between 10 and 15 per cent of Cushing's-related pituitary tumours grow to sizes in excess of 1 centimetre in diameter, which is larger than average. These tumours, or macroadenomas, present a secondary set of problems unrelated to Cushing's by putting pressure on brain tissue and nerves. Afflicted dogs can present with seizures and other neurological symptoms.
Seizures follow an abnormal surge of electrical activity in the brain and can spread from point of origin, such as the pituitary tumours that cause spontaneous Cushing's. Pituitary tumours trigger focal motor (partial) seizures that are similar to grand mal seizures. Grand mal seizures usually last two minutes or less and are preceded by a period of abnormal behaviour characterised by vocalisation, restlessness and anxiety, clingy behaviour or seclusion. During the seizure itself, the dog collapses, slips into unconsciousness and, sometimes, stops breathing for a period of 10 to 30 seconds. After this point, the legs may jerk rhythmically. In focal motor seizures, this jerking is confined to a specific area of the body.
Do not move a seizing dog unless it is in a dangerous location, as any physical movement could trigger further seizures. This prohibition includes manipulating the dog's mouth to prevent it from swallowing its tongue. Dogs cannot swallow their tongues.
Contact your veterinarian as soon as the seizure stops, as she will surely want to examine your dog for the cause of the seizure. Note and inform your veterinarian how long the seizure lasts, as any seizure or seizure cluster lasting longer than five minutes are emergencies that can be fatal. Your dog will need intravenous Valium or anticonvulsants to prevent permanent brain damage or death.
Spontaneous Cushing's Treatments
No sufficient body of evidence exists to promote medical treatment of spontaneous Cushing's as a viable tool for extending the lifespan of an affected dog. Experts consider medical treatment optional if a Cushing's patient is free of symptoms that interfere with its quality of life.
Surgical treatment is available to patients with either pituitary or adrenal gland tumours. The success rate (measured as survival 16 months after surgery) is about 50 per cent, which is virtually the same as that of medical therapy.
Patients with active Cushing's symptoms who do not undergo surgery to remove the actual cause of the illness (the tumour) can be treated with certain medications that will at least control the symptoms. Anipryl is used to treat pituitary-dependent Cushing's; mitotane is used for adrenal Cushing's. With either medication, treatment is tailored to the individual patient and closely monitored by the veterinarian.