Write a short note on hypoglycaemia.

Definition

Hypoglycaemia is defined by Whipple's triad:

1. Symptoms consistent with hypoglycaemia

2. A low plasma glucose concentration measured at the time of symptoms

3. Relief of symptoms when glucose is raised

In diabetic practice, a glucose below 70 mg/dL is the alert value requiring action; below 54 mg/dL indicates clinically significant hypoglycaemia; and severe hypoglycaemia is any episode requiring the assistance of another person, regardless of the value.

Causes

In diabetics (far commoner):

• Excess insulin or sulphonylurea — dose error, or dose unchanged when requirements fall
• Missed or delayed meal, or reduced carbohydrate intake
• Unaccustomed exercise (effect may be delayed for many hours)
• Alcohol — inhibits gluconeogenesis, and blunts awareness
• Renal or hepatic impairment — reduced insulin clearance and gluconeogenesis; a common cause of prolonged hypoglycaemia in the elderly
• Recovery from an intercurrent illness or withdrawal of corticosteroids

In non-diabetics:

• Insulinoma — fasting hypoglycaemia with inappropriately high insulin and C-peptide
• Drugs — quinine, quinolones, beta-blockers (which also mask symptoms), pentamidine, salicylates
• Endocrine — adrenal insufficiency, hypopituitarism, hypothyroidism
• Critical illness — sepsis, hepatic failure, renal failure, malnutrition
• Post-prandial (reactive) hypoglycaemia; post-bariatric surgery
• Non-islet cell tumours producing IGF-2; autoimmune insulin syndrome
• Factitious — surreptitious insulin or sulphonylurea administration
• Alcohol with starvation; falciparum malaria and its treatment with quinine — important in India

Clinical Features

Autonomic (early, glucose ~60–70 mg/dL) — mediated by adrenergic and cholinergic activation, and serving as the warning system:

Sweating, tremor, palpitations, anxiety, hunger, tingling, pallor.

Neuroglycopenic (later, glucose < 50 mg/dL) — from cerebral glucose deprivation:

Difficulty concentrating, confusion, slurred speech, behavioural change and aggression, drowsiness, visual disturbance, focal neurological deficit mimicking stroke, seizures, and coma.

In the elderly, presentation is often atypical — falls, confusion or "stroke-like" episodes — and hypoglycaemia is easily misattributed to dementia or cerebrovascular disease.

Hypoglycaemia Unawareness

Repeated hypoglycaemia blunts the autonomic warning response, so patients progress to neuroglycopenia without warning symptoms. It is associated with long duration of type 1 diabetes, tight control, autonomic neuropathy, and beta-blocker use. Scrupulous avoidance of hypoglycaemia for several weeks can restore awareness — this is why targets are relaxed in such patients.

Investigations

In a diabetic, no investigation beyond confirming the glucose and identifying the cause is usually needed.

In a non-diabetic, document Whipple's triad and take a "hypoglycaemia screen" at the time of hypoglycaemia, before treatment: plasma glucose, insulin, C-peptide, pro-insulin, beta-hydroxybutyrate, sulphonylurea screen, cortisol and growth hormone.

A 72-hour supervised fast remains the definitive test for insulinoma, followed by localisation with CT, MRI, endoscopic ultrasound or Ga-68 DOTANOC PET.

Management

Conscious and able to swallow — the "rule of 15":

Give 15–20 g of rapid-acting carbohydrate (glucose tablets, 3–4 teaspoons of sugar or honey in water, or half a glass of fruit juice or regular soft drink), recheck after 15 minutes, and repeat if still low. Follow with a long-acting carbohydrate (a meal, bread, banana) to prevent recurrence.

Unconscious or unable to swallow:

• Intravenous dextrose — 25% or 50% dextrose as a bolus, followed by a 10% dextrose infusion where recurrence is likely.
• Glucagon intramuscularly where intravenous access is unavailable — but note it is ineffective in starvation, alcohol excess and liver disease, where glycogen stores are depleted.
• Recheck glucose after 10–15 minutes and repeat as needed; give carbohydrate once the patient is alert.

After the episode:

• Identify and correct the cause — review the insulin or sulphonylurea dose, meal pattern, renal function and alcohol intake; re-educate on sick-day rules and exercise.
• Sulphonylurea-induced and long-acting insulin-induced hypoglycaemia require prolonged observation and a dextrose infusion, often for 24–48 hours, because relapse after apparent recovery is the rule. Octreotide may be used for refractory sulphonylurea hypoglycaemia.
• Ensure the patient carries glucose and identification, and that family members know how to recognise and treat episodes.