Page 857 - Small Animal Internal Medicine, 6th Edition

CHAPTER 49 Disorders of the Endocrine Pancreas 829

into the lens, leading to swelling and rupture of lens fibers examination findings include pelvic limb paresis, abnormal
and the development of cataracts. Cataract formation is an gait, knuckling, decreased muscle tone, muscle atrophy,
VetBooks.ir irreversible process once it begins, and it can occur rapidly. depressed limb reflexes, and deficits in postural reaction
testing. Diabetic neuropathy in the dog is primarily a distal
Diabetic dogs that are poorly controlled and have problems
with wide fluctuations in blood glucose concentrations seem
and axonal degeneration. Electrodiagnostic abnormalities
especially at risk for rapid development of cataracts. Good polyneuropathy, characterized by segmental demyelination
glycemic control and minimal fluctuation in the blood include spontaneous sharp waves and fibrillation potentials
glucose concentration prolongs the onset of cataract forma- and decreased M-wave amplitude on electromyogram and
tion. Once blindness occurs as a result of cataract formation, decreased motor and sensory nerve conduction velocities.
the need for stringent blood glucose control is reduced. No specific treatment for diabetic neuropathy is known
Blindness may be eliminated by removing the abnormal besides meticulous metabolic control of the diabetic state.
lens. Vision is restored in approximately 80% of diabetic
dogs that undergo cataract removal. Factors that affect the Diabetic Nephropathy
success of surgery include the degree of glycemic control Diabetic nephropathy has occasionally been reported in the
preceding surgery, the presence of retinal disease, and the dog. Diabetic nephropathy is a microvascular disease involv-
presence of lens-induced uveitis. Acquired retinal degenera- ing the capillary and precapillary arterioles, and is mani-
tion affecting vision is more of a concern in older diabetic fested mainly by thickening of the capillary basement
dogs than diabetic retinopathy. Fortunately, acquired retinal membrane. Histopathologic findings include membranous
degeneration is unlikely in an older diabetic dog with vision glomerulonephropathy, glomerular and tubular basement
immediately before cataract formation. If available, electro- membrane thickening, an increase in the mesangial matrix
retinography should be performed before surgery to evaluate material, and the presence of subendothelial deposits, glo-
retinal function. merular fibrosis, and glomerulosclerosis. Glucose plays a
central role in the development of microvascular damage.
Lens-Induced Uveitis Clinical signs depend on the severity of glomerulosclerosis
During embryogenesis the lens is formed within its own and the functional ability of the kidney to excrete metabolic
capsule, and its structural proteins are not exposed to the wastes. Initially, diabetic nephropathy is manifested as pro-
immune system. Therefore immune tolerance to the crystal- teinuria, primarily albuminuria. As glomerular changes pro-
line proteins does not develop. During cataract formation gress, glomerular filtration becomes progressively impaired,
and reabsorption, lens proteins are exposed to the local resulting in the development of azotemia and eventually
immune system, resulting in inflammation and uveitis. uremia. With severe fibrosis of the glomeruli, oliguric and
Uveitis that occurs in association with a reabsorbing, hyper- anuric kidney failure may develop.
mature cataract may decrease the success of cataract surgery Monitoring urine for the presence of microalbumin-
and must be controlled before surgery. Treatment of lens- uria is used as an early marker for development of diabetic
induced uveitis focuses on decreasing inflammation and nephropathy in diabetic humans. Microalbuminuria occurs
preventing further intraocular damage. Topical ophthalmic in diabetic dogs, and increased urine albumin:creatine ratios
glucocorticoids (e.g., prednisone acetate) are the most com- precede increased urine protein:creatinine ratios. In one
monly used drug for the control of ocular inflammation. study, 11 (55%) of 20 diabetic dogs had an increase in the
However, systemic absorption of topically applied glucocor- urine albumin:creatinine ratio, and only 6 of these 11 dogs
ticoids may cause insulin resistance and interfere with gly- also had an increase in urine protein:creatinine ratio, sug-
cemic control of the diabetic state, especially in toy and gesting that monitoring urine albumin:creatinine ratio may
miniature breeds. An alternative is the topical administra- be of value as an early marker for kidney disease in diabetic
tion of nonsteroidal antiinflammatory agents such as diclo- dogs (Mazzi et al., 2008). However, the predictive value of
fenac (Voltaren) or flurbiprofen ophthalmic (Ocufen). microalbuminuria for diabetic nephropathy and the clinical
Although not as potent an antiinflammatory agent as gluco- relevance of microalbuminuria in diabetic dogs remains to
corticoids, nonsteroidal antiinflammatory drugs should not be clarified. Diabetic nephropathy is a significant chronic
interfere with glycemic control. complication in diabetic humans that takes years to pro-
gress to chronic end-stage kidney disease; a time line that
Diabetic Neuropathy may explain why clinically relevant diabetic nephropathy is
Although a common complication in the diabetic cat (see uncommon in diabetic dogs. Regardless, proteinuria, kidney
p. 833), diabetic neuropathy is infrequently recognized in function, and systemic blood pressure should be monitored
the diabetic dog. Subclinical neuropathy is probably more in diabetic dogs that have developed microalbuminuria.
common than is severe neuropathy resulting in clinical signs. No specific treatment for diabetic nephropathy is known,
Clinical signs consistent with diabetic neuropathy are most apart from meticulous metabolic control of the diabetic
commonly recognized in dogs that have been diabetic for a state, conservative medical management of kidney disease,
long time (i.e., 5 years or longer), although diabetic neuropa- administration of angiotensin-converting enzyme (ACE)
thy has been diagnosed in dogs shortly after the diagnosis inhibitors to minimize proteinuria, and control of systemic
of diabetes has been established. Clinical signs and physical hypertension.