Cushing's disease typically appears in middle-aged to older dogs, affecting an estimated 100,000 dogs per year in the United States. Cushing's involves the dog's adrenal glands and is the result of the production of excessive cortisol, the stress hormone responsible for converting fat and muscle tissue into glucose under stressful conditions.
Typical Cushing's Symptoms
Dogs with Cushing's disease will experience a sudden increase in appetite and thirst level, often to the point of becoming incontinent in the house. A pot belly may develop and the dog may experience a loss of muscle tone in the hind end, accompanied by noticeable weakness in the hind end. Dogs may show sporadic shedding or shed their fur in clumps, usually equally on each side of the body. In contrast, the dog may develop very thick hair. Since prolonged exposure can cause lasting damage to a dog's body, he also may develop diabetes, pancreatitis, bladder stones, hypertension, kidney disease, urinary tract or bladder infections, pulmonary thromboembolism or congestive heart failure as a result of Cushing's disease.
Sudden Acquired Retinal Degeneration
Sudden acquired retinal degeneration syndrome (SARDS) shares some of the same symptoms as Cushing's, such as a noticeably increased appetite and water consumption. Like Cushing's, SARDS appears in older dogs, usually between 7 and 14 years of age. The affliction can strike any pure or mixed-breed dog, and is more prevalent in females than in males. Onset typically is sudden, with noticeable symptoms appearing as quickly as overnight, or over a period of 5 to 10 days.
Physiological Changes and SARDS
Dog owners usually notice a dramatic increase in a dog's appetite and water consumption in the weeks leading up to vision loss. Many times the dog will gain weight, and some owners also report a loss in smell and hearing as well as vision. SARDS is the result of the destruction of the rods and cones in the visual cell layer of the eye's retina, causing blindness. When examined by a veterinarian, the retina usually appears normal, but the pupil will be dilated and unresponsive to light. In some cases, pupil reaction will be present but sluggish. Dogs with SARDS fail to visually track objects placed before them.
Blood and urine lab work in dogs with SARDS many times shows changes associated with Cushing's disease. These dogs then also should have follow-up testing for Cushing's. Those with laboratory results indicative of Cushing's should receive treatment for the disease. Although treatment will alleviate the symptoms of Cushing's, vision typically does not return.