Which is not true of hypocalcaemia:
**Core Concept**
Hypocalcemia refers to a serum calcium level below 2.2 mmol/L, which can lead to various clinical manifestations due to the critical role of calcium in neuromuscular excitability, muscle contraction, and vascular tone. The pathophysiology of hypocalcemia involves impaired parathyroid hormone (PTH) secretion or action, vitamin D deficiency, or increased calcium excretion.
**Why the Correct Answer is Right**
Hypocalcemia is characterized by clinical features such as muscle cramps, tetany, carpopedal spasm, and cardiac arrhythmias, particularly QT interval prolongation. The increased neuromuscular excitability in hypocalcemia is due to the reduced calcium-dependent inhibition of the N-type calcium channels in the presynaptic neuron, leading to an excessive release of neurotransmitter. This results in muscle contraction and tetany.
**Why Each Wrong Option is Incorrect**
**Option A:** This statement might be true or false depending on the context, so we can't assess its accuracy without more information.
**Option B:** This statement might be true, as hypocalcemia can indeed cause muscle cramps and tetany due to increased neuromuscular excitability.
**Option C:** This statement is false because hypocalcemia is characterized by reduced neuromuscular excitability, not increased.
**Clinical Pearl / High-Yield Fact**
In the clinical setting, hypocalcemia can be diagnosed using the Chvostek sign, which is characterized by twitching of the facial muscles in response to tapping the facial nerve in front of the ear. This sign is a useful indicator of hypocalcemia.
**Correct Answer: C. This statement is false because hypocalcemia is characterized by reduced neuromuscular excitability, not increased.**