Introduction to Cushing's disease

Introduction Hyperadrenocorticism results from the production of excessive glucocorticoids (Cushing's disease) from one or both adrenal glands, or from long-term or excessive administration of steroid drugs (Cushing's syndrome). In atypical cases, other adrenal hormones may also be elevated, such as sex hormones. Causes of the disease When the pituitary tumor produces high levels of adrenocorticotropic hormone (ACTH), which causes the adrenal gland to become overactive, it develops into pituitary-resistant adrenal hyperfunction (PDH). PDH in dogs is the most common cause of Cushing's disease (85%). The vast majority of pituitary tumors are small (microadenomas) and do not cause neurological symptoms, but the proportion of large tumors (large adenomas) can reach 30%. Because ACTH can affect the bilateral adrenal glands, this type of disease usually leads to an enlargement of the bilateral adrenal glands. The proportion of dogs with adrenal tumors is 15%, and half of them are malignant tumors. Usually, only the unilateral adrenal gland is affected and increases. Long-term or excessive use of glucocorticoids (such as prednisone, dexamethasone, hydrocortisone, fludroxtonone or methylprednisolone) can lead to iatrogenic adrenal hyperfunction. Because the pituitary gland often detects high levels of steroids in the blood, it reduces the production of ACTH, leading to bilateral adrenal atrophy. Most of the clinical symptoms of dogs are middle-aged or older dogs. Mini VIPs, Dachshunds, Boxer Dogs, Boston Terriers, and Beagle dogs are susceptible to the disease. Adrenal tumors are more common in female large dogs. Common clinical symptoms are as follows: polydipsia, polyuria, appetite increase obesity ("bucket belly" appearance), lethargy, muscle weakness, hair symmetry reduction or shedding, especially skin thinning or pigmentation in the trunk area, skin easily scratches asthma Uncommon clinical symptoms of refractory urethra and skin infections include hypertension and ocular bleeding, infertility, congestive heart failure, acute respiratory problems caused by pulmonary blood clots, and knee ligament rupture. Diagnostic tests are based on a history of long-term use of steroids. Cushing's syndrome is often suspected. A laboratory test reveals a decrease in adrenal function (low cortisol levels, no response to the ACTH stimulation test). The diagnosis of Cushing's disease requires laboratory and other tests because the disease has no specific clinical symptoms. Routine examinations may show elevated liver enzymes, cholesterol, blood sugar and white blood cells. Urine analysis and urine culture can reveal infection. Several screening tests are available that involve the determination of blood cortisol levels. They include low-dose dexamethasone inhibition test, ACTH stimulation test, urinary cortisol/creatinine ratio, and modified high-dose dexamethasone inhibition test. The vast majority of these trials require blood samples to be taken at regular intervals. Once the diagnosis of Cushing's disease is temporarily obtained, it is necessary to determine which type (PDH or adrenal tumor). High-dose dexamethasone suppression tests, blood ACTH measurements, abdominal X-rays, adrenal ultrasound, and pituitary magnetic resonance imaging help identify these two types of diseases. Cushing's disease is difficult to diagnose because the test results may not be so clear. A diagnosis may require multiple tests or multiple tests. Treatment The treatment of Cushing's syndrome can be achieved by slowly reducing the amount of steroids. It is not possible to stop the drug quickly because it takes some time for the adrenal gland to start producing hormones again. Sudden withdrawal of steroids can lead to acute adrenal insufficiency. PDH is the most commonly used drug treatment, namely Lysodren. Ketoconazole and L-deprenyl can be used in some cases, but usually do not work well. Radiotherapy for certain pituitary tumors may also be considered. Adrenal tumors may be surgically removed or may be treated with mitoxantrone or trilostane. Surgery is the most successful when the tumor involves only one side of the adrenal gland and does not invade the blood vessels of the surrounding aorta or kidney. Postoperative care is a challenge because sometimes another adrenal gland usually does not secrete normal levels of hormones. Malignant tumors can also be transferred to other parts of the body. The treatment of follow-up care for this disease is quite complex, requiring frequent adjustments to the drug dose and repeated laboratory tests, which is costly. In addition, the therapeutic drugs are potentially toxic, and the efficacy of mitoxant will continue for several days after stopping the drug. Therefore, it is important to fully understand the effects and side effects of these drugs. Prognosis Although most PDH dogs will improve after treatment, not all clinical abnormalities are reversible, and the disease can shorten the life span of dogs.