Diabetes Mellitus in Dogs and Cats

Overview

Pathophysiology

Dogs — Type 1–like (Insulin-Dependent DM)

• Most canine DM resembles human Type 1 DM: progressive immune-mediated or idiopathic destruction of pancreatic β-cells leads to absolute insulin deficiency.
• Other contributing causes include chronic pancreatitis (most common concurrent disease), diestrus-related progesterone excess (in intact females), and concurrent hyperadrenocorticism (Cushing's disease).
• Progesterone stimulates growth hormone (GH) secretion from mammary tissue, inducing peripheral insulin resistance, which can permanently damage β-cells if prolonged.
• Result: these dogs almost always require lifelong exogenous insulin.

Cats — Type 2–like (Non-Insulin-Dependent initially)

• Feline DM more closely resembles human Type 2 DM: a combination of peripheral insulin resistance and relative β-cell dysfunction.
• Key pathological feature: islet amyloid deposition (amylin/IAPP deposits) in the pancreas — identical to human T2DM — causes progressive β-cell loss.
• Obesity is the single biggest risk factor — obese cats have 4× the risk of diabetic cats.
• Other risk factors: male sex (neutered males most affected), glucocorticoid or progestogen administration, hypersomatotropism (acromegaly due to pituitary GH excess — present in ~25–30% of diabetic cats), chronic pancreatitis.
• A critical feature unique to cats: diabetic remission — if insulin resistance is eliminated (e.g., weight loss, discontinuation of steroids, treatment of acromegaly) and β-cells recover, cats may go into complete remission and no longer require insulin. Remission rates of 50–80% are achievable with tight glycemic control.

Signalment and Epidemiology

Clinical Signs

• Polyuria (PU) — osmotic diuresis from glycosuria
• Polydipsia (PD) — compensatory
• Polyphagia — cellular starvation despite hyperglycemia
• Weight loss — catabolism of fat and muscle

Additional Dog-Specific Signs

• Cataracts — very common in dogs (sorbitol accumulation in the lens); often the presenting complaint; can develop rapidly (days to weeks)
• Hepatomegaly (lipid hepatopathy)
• Bilateral cataracts are nearly pathognomonic for DM in dogs

Additional Cat-Specific Signs

• Peripheral neuropathy — plantigrade stance (walking on hocks), weakness; unique to cats among domestic animals
• Cataracts are rare in cats
• Hepatic lipidosis may develop, especially in anorexic cats
• Muscle wasting, unkempt coat

Diagnosis

Criteria

• Fructosamine: reflects mean BG over the past 2–3 weeks (normal <340 µmol/L in cats); elevated in true DM
• HbA1c: less useful in cats (short feline RBC lifespan); fructosamine is preferred

Minimum Database

• CBC, serum chemistry panel (look for concurrent pancreatitis, hepatic disease, UTI, Cushing's)
• Urinalysis + urine culture (UTIs are common and can cause insulin resistance)
• Fructosamine (especially in cats)
• Abdominal ultrasound — assess pancreas, adrenal glands, liver
• In cats: IGF-1 level to screen for acromegaly (>1000 ng/mL suspicious; >1600 ng/mL highly suggestive); pituitary MRI if acromegaly confirmed

Treatment

Dietary Management

• High-fiber, complex carbohydrate diet helps blunt postprandial glucose spikes
• Consistent feeding times timed to insulin injection are critical
• Avoid high-fat diets (pancreatitis risk)

• Low-carbohydrate, high-protein diet (wet/canned food preferred) is the cornerstone of feline DM management
• Reduces postprandial hyperglycemia dramatically
• Can facilitate diabetic remission
• Target: <10% of calories from carbohydrates (most dry kibbles are 30–40% carbohydrate)

Insulin Therapy

• Starting dose: typically 0.25 U/kg BID, fed simultaneously with injection
• Goal: glucose nadir 80–150 mg/dL, pre-insulin glucose 150–250 mg/dL

• Glargine + low-carb diet achieves remission in ~50–80% of newly diagnosed cats
• BID dosing is preferred in cats regardless of insulin type

Monitoring

• Serial BG measurements every 1–2 hours over 10–12 hours
• Assess: nadir, duration of action, Somogyi rebound
• Target nadir: 80–150 mg/dL (dogs), 80–150 mg/dL (cats)
• Avoid nadir <60 mg/dL (hypoglycemia risk)

• Strongly recommended, especially in cats (eliminates stress hyperglycemia artifact)
• Glucometers calibrated for cats/dogs (e.g., AlphaTrak) — human glucometers underestimate feline BG by ~10–15%
• Continuous glucose monitors (Libre) increasingly used in veterinary practice

• Useful for long-term assessment; target <400–450 µmol/L in well-controlled diabetics

Complications

Diabetic Ketoacidosis (DKA)

• Most serious acute complication; occurs in both species
• Absolute insulin deficiency → fat mobilization → ketone body production (acetoacetate, β-hydroxybutyrate) → metabolic acidosis
• Triggered by concurrent illness (infection, pancreatitis, neoplasia)
• Signs: vomiting, anorexia, lethargy, dehydration, Kussmaul breathing, "fruity" breath odor, collapse
• Treatment: IV fluid resuscitation (0.9% NaCl), correction of electrolyte abnormalities (K⁺, phosphate critically important), regular (short-acting) insulin CRI or hourly IM injections until stable, treat underlying trigger
• Potassium falls rapidly with insulin therapy — monitor q2–4h; supplement aggressively

Hyperosmolar Hyperglycemic State (HHS)

• Extreme hyperglycemia (>600 mg/dL), severe dehydration, hyperosmolarity, without significant ketosis
• More common in cats; high mortality
• Treatment: very slow fluid rehydration (avoid cerebral edema), cautious insulin use

Hypoglycemia

• Iatrogenic (insulin overdose) — can be life-threatening
• Signs: weakness, ataxia, tremors, seizures, coma
• Treatment: oral glucose (if conscious) or IV dextrose bolus (50% dextrose 0.5 mL/kg diluted to 25% and given slowly IV)

Cataracts (Dogs)

• Rapid formation; sorbitol and fructose accumulate in the lens by an insulin-independent pathway
• Can lead to lens-induced uveitis and glaucoma
• Surgical removal (phacoemulsification) is effective if performed before uveitis becomes chronic

Peripheral Neuropathy (Cats)

• Demyelination of peripheral nerves
• Plantigrade posture (dropped hocks) in hindlimbs
• May partially or fully resolve with good glycemic control or diabetic remission
• B-vitamin supplementation (B12, B1) may be helpful adjunctively

Urinary Tract Infections

• Common in both species due to glucosuria providing a substrate for bacterial growth
• Often subclinical — routine urine culture every 3–6 months is recommended
• Important cause of insulin resistance/poor glycemic control

Chronic Pancreatitis

• Both a cause and consequence of DM in dogs and cats
• Perpetuates β-cell destruction and insulin resistance
• Management: low-fat diet (dogs), hydration, analgesia, anti-emetics

Prognosis

• Early diagnosis and immediate tight glycemic control
• Low-carbohydrate diet adherence
• Treating underlying insulin resistance (obesity, acromegaly, steroids)
• Home BG monitoring

Special Considerations

Intact Female Dogs

• Diestrus and pregnancy cause progesterone-driven GH excess and insulin resistance
• Ovariohysterectomy (OHE) at the time of diagnosis is strongly recommended in intact females — can lead to remission in early cases before irreversible β-cell loss
• Prevents recurrence in subsequent diestrus cycles

Acromegaly in Cats

• Pituitary GH-secreting adenoma causes IGF-1 excess → profound insulin resistance
• Insulin requirements can be enormous (>10 U/cat BID or more) with poor control
• Diagnosis: elevated IGF-1 + pituitary mass on MRI/CT
• Treatment: radiation therapy (stereotactic radiosurgery), hypophysectomy; medical options (octreotide, cabergoline) are inconsistent
• With successful treatment, insulin requirements drop dramatically and remission is possible

Concurrent Hyperadrenocorticism in Dogs

• Cushing's disease causes cortisol-driven insulin resistance
• Treat Cushing's (trilostane or mitotane) alongside DM; insulin requirements will decrease as cortisol normalizes
• Important not to reduce insulin too slowly as Cushing's resolves — hypoglycemia risk

Summary Comparison Table