MCQ – 99890

Tetany may be a feature of all of the following except:

Correct Answer � D Explanation

Tetany refers to involuntary muscle contractions and spasms due to increased neuromuscular excitability. It typically results from electrolyte imbalances that affect the resting membrane potential and calcium availability at the neuromuscular junction.

Evaluation of Each Option:

A. Hyperventilation

• Leads to respiratory alkalosis, which increases binding of calcium to albumin, reducing ionized (free) calcium levels.

• This hypocalcemia is functionally significant and may trigger tetany, paresthesia, and carpopedal spasms.

B. Hypokalaemic alkalosis

• Alkalosis contributes to hypocalcemia, and hypokalemia increases neuromuscular excitability.

• The combination often presents with tetany and muscle cramps.

C. Hypomagnesaemia

• Magnesium is essential for PTH secretion and function.

• Severe hypomagnesemia can lead to hypocalcemia, causing tetany.

• It can also directly increase neuromuscular excitability.

D. Hyponatraemia

• While hyponatraemia can cause neurological symptoms (e.g., headache, confusion, seizures), it does not typically cause tetany.

• It affects cerebral edema and neuronal swelling, not the calcium-dependent neuromuscular junction.