Canine Diabetes Mellitus Study Guide

Overview and Clinical Importance

Diabetes mellitus (DM) is a common endocrine disorder in dogs characterized by persistent hyperglycemia and glucosuria resulting from an absolute or relative deficiency of insulin. The condition affects approximately 0.3-0.5% of the canine population and is one of the most frequently tested endocrine topics on the NAVLE.

Unlike cats, where Type 2 (insulin-resistant) diabetes predominates, most diabetic dogs suffer from insulin-deficient diabetes analogous to human Type 1 diabetes. This results from destruction of pancreatic beta cells through immune-mediated processes, chronic pancreatitis, or idiopathic mechanisms. Consequently, lifelong insulin therapy is the mainstay of treatment, and diabetic remission is rare in dogs.

Etiology and Pathophysiology

Classification of Canine Diabetes

Canine diabetes is heterogeneous with multiple underlying pathological processes converging on insulin deficiency:

Type 1 / Insulin-Deficient Diabetes (Most Common)

• Results from destruction of pancreatic beta cells leading to absolute insulin deficiency
• Mechanisms include immune-mediated beta cell destruction, chronic pancreatitis, and idiopathic beta cell atrophy
• Requires lifelong insulin therapy; remission is extremely rare
• Studies show approximately 50% of diabetic dogs have histological evidence of chronic pancreatitis at necropsy

Diestrus Diabetes (Gestational Diabetes)

• Occurs in intact female dogs during diestrus due to progesterone-induced growth hormone secretion from mammary tissue
• Progesterone and growth hormone antagonize insulin action, causing insulin resistance
• May be reversible if ovariohysterectomy is performed early before permanent beta cell damage occurs
• Particularly common in Scandinavian breeds (Elkhounds, Lapphunds)

Secondary Diabetes

• Results from concurrent diseases causing insulin resistance: hyperadrenocorticism (Cushing's disease), acromegaly, hypothyroidism
• Drug-induced: prolonged glucocorticoid or progestogen therapy
• May improve or resolve with treatment of underlying condition

Breed Predisposition and Risk Factors

Genetic factors play a significant role in canine diabetes susceptibility. Research has identified associations with dog leukocyte antigen (DLA) genes similar to HLA associations in human Type 1 diabetes.

Additional Risk Factors

• Age: Middle-aged to older dogs (7-9 years peak incidence); rarely occurs under 1 year of age
• Sex: Intact females 2x more likely due to diestrus-associated insulin resistance
• Body Condition: Obesity contributes to insulin resistance but is less causative than in cats
• Concurrent Disease: Chronic pancreatitis, hyperadrenocorticism, infections

Clinical Presentation

Classic Clinical Signs (The "Four Ps")

Additional Clinical Findings

• Cataracts: 50% of diabetic dogs develop cataracts within 6 months, 80% within 16 months (even with good glycemic control)
• Hepatomegaly: Due to hepatic lipidosis from altered fat metabolism
• Recurrent infections: UTIs, skin infections, periodontal disease common due to impaired neutrophil function
• Poor coat quality: Dull, dry, flaky coat in chronic cases
• Plantigrade stance: Rare in dogs (common in cats) - indicates diabetic neuropathy

Diagnosis

Diagnostic Criteria

Diagnosis of diabetes mellitus requires documentation of BOTH persistent fasting hyperglycemia AND glucosuria in conjunction with appropriate clinical signs.

Minimum Database for New Diabetic Diagnosis

• Complete Blood Count (CBC): May show stress leukogram; evaluate for concurrent infection
• Serum Biochemistry Profile: Hyperglycemia, hypercholesterolemia, elevated liver enzymes (ALP, ALT), azotemia in dehydrated patients
• Urinalysis with Culture: Glucosuria, +/- ketonuria, assess for UTI (common concurrent finding)
• Serum Fructosamine: Differentiates true diabetes from stress hyperglycemia; reflects average glucose over 2-3 weeks
• Additional Testing: Consider thyroid panel, spec cPL (pancreatitis), cortisol testing if concurrent disease suspected

Treatment

Goals of Therapy

• Eliminate clinical signs (PU/PD, polyphagia, weight loss)
• Avoid hypoglycemia (the most dangerous acute complication of insulin therapy)
• Maintain blood glucose between 100-250 mg/dL throughout the day
• Achieve a glucose nadir between 80-150 mg/dL
• Maintain good quality of life for patient and owner

Insulin Therapy

Insulin is the cornerstone of canine diabetes management. Selection should be based on duration of action, availability, and patient response.

Dietary Management

• High fiber diets: Slow glucose absorption, improve glycemic control; recommended for most diabetic dogs
• Consistent feeding: Feed equal portions at same times daily, ideally before or with insulin injection
• Avoid simple sugars: Semi-moist foods contain propylene glycol which causes rapid glucose spikes
• Weight management: Obese dogs should undergo gradual weight loss to reduce insulin resistance
• Intact females: Recommend ovariohysterectomy to eliminate diestrus-associated insulin resistance

Monitoring

Blood Glucose Curve

The blood glucose curve is the gold standard for evaluating insulin effectiveness. Blood glucose is measured every 2 hours for 10-12 hours after insulin administration and feeding.

Fructosamine Interpretation

• Less than 350 μmol/L: Excellent glycemic control (or possible hypoglycemia)
• 350-400 μmol/L: Good control
• 400-500 μmol/L: Fair control
• Greater than 500 μmol/L: Poor control - reassess therapy
• Greater than 600 μmol/L: Severe lack of control - urgent reassessment needed

Complications

Diabetic Ketoacidosis (DKA)

DKA is a life-threatening emergency occurring when severe insulin deficiency leads to uncontrolled lipolysis and ketone body production. It requires intensive hospitalization with fluid therapy and insulin administration.

Pathophysiology

Without insulin, cells cannot utilize glucose and switch to fat metabolism. The liver converts free fatty acids to ketone bodies (acetoacetate, beta-hydroxybutyrate, acetone). Accumulation of these acidic ketones causes metabolic acidosis, electrolyte imbalances, and severe dehydration from osmotic diuresis.

Clinical Signs

• Vomiting, anorexia, lethargy, weakness
• Severe dehydration, tachypnea (Kussmaul breathing)
• Sweet/fruity breath (acetone)
• Abdominal pain (concurrent pancreatitis common)
• Obtundation, coma in severe cases

Diagnostic Criteria

• Hyperglycemia: Blood glucose often greater than 500 mg/dL
• Ketonemia/Ketonuria: Blood ketones greater than 3.8 mmol/L diagnostic for DKA in dogs
• Metabolic Acidosis: pH less than 7.3, decreased bicarbonate
• Electrolyte Abnormalities: Hypokalemia (total body K+ depleted), hypophosphatemia common

Treatment Protocol

• Aggressive IV Fluid Therapy: 0.9% NaCl initially to restore circulating volume; correct dehydration over 12-24 hours
• Regular Insulin Therapy: IV CRI at 2.2 U/kg/day or IM hourly injections; short-acting insulin allows precise control
• Potassium Supplementation: Critical - insulin drives K+ into cells, worsening hypokalemia; supplement based on serum levels
• Dextrose Supplementation: Add 2.5-5% dextrose to fluids when glucose falls below 250 mg/dL to prevent hypoglycemia while continuing insulin
• Frequent Monitoring: Blood glucose every 1-2 hours, electrolytes every 4-6 hours initially
• Identify and Treat Triggers: Pancreatitis, UTI, pneumonia, hyperadrenocorticism commonly trigger DKA

Diabetic Cataracts

Cataracts are the most common complication of canine diabetes. Approximately 80% of diabetic dogs develop cataracts within 16 months of diagnosis, regardless of glycemic control.

Pathophysiology

Excess glucose enters the lens via aqueous humor. The enzyme aldose reductase converts glucose to sorbitol, which cannot exit the lens. Sorbitol accumulation causes osmotic water influx, lens fiber swelling and disruption, and rapid cataract formation. This process can occur over weeks.

Clinical Progression

• 50% develop cataracts within 6 months of diagnosis
• 75% within 12 months
• 80% within 16 months
• Cataracts typically form rapidly ("intumescent cataracts") and progress to maturity quickly

Lens-Induced Uveitis

As cataracts mature and the lens swells, lens proteins leak through the capsule, causing severe intraocular inflammation (phacolytic uveitis). If the capsule ruptures (phacoclastic uveitis), inflammation intensifies dramatically. Complications include secondary glaucoma, lens luxation, and retinal detachment.

Management

• Topical NSAIDs: Start as soon as cataract detected to prevent/control lens-induced uveitis
• Early ophthalmology referral: Cataract surgery (phacoemulsification) has 90-95% success rate when performed early
• Surgical considerations: Success rate decreases with preoperative uveitis; requires stable diabetic control

Hypoglycemia

Hypoglycemia is the most dangerous acute complication of insulin therapy and can be life-threatening. It usually results from insulin overdose, missed meals, or increased exercise.

Clinical Signs

• Mild: Weakness, lethargy, hunger, trembling
• Moderate: Ataxia, disorientation, behavior changes
• Severe: Seizures, coma, death

Emergency Treatment

• At home: Rub corn syrup/honey on gums (1 tbsp per 5 lbs body weight); offer food when alert
• In clinic: IV dextrose bolus (0.5-1 mL/kg of 50% dextrose diluted 1:4); continue dextrose supplementation as needed

Prognosis

With appropriate management, many diabetic dogs can live good quality lives for years. Survival depends heavily on owner commitment and management of concurrent diseases.

• Median survival time: Approximately 2-3 years from diagnosis with treatment
• Day 1 euthanasia: Up to 25% of dogs are euthanized at diagnosis - often due to lack of owner education about manageability
• Negative prognostic factors: DKA at presentation, concurrent pancreatitis, hyperadrenocorticism, severe cataracts with glaucoma
• Positive factors: Dedicated owner, uncomplicated diabetes, good initial response to insulin