Which electrolyte disturbance presents with absent deep tendon reflexes and hypotension in severe cases?

• A. Hyperkalemia
• B. Hyponatremia
• C. Hypocalcemia
• D. Hypermagnesemia

Answer: (D)

High magnesium levels depress neuromuscular transmission. Magnesium acts as a calcium channel blocker at the neuromuscular junction, reducing acetylcholine release and dampening motor neuron excitability, which leads to diminished or absent deep tendon reflexes. As magnesium accumulates, it also causes smooth muscle relaxation and vasodilation, resulting in hypotension; severe cases can progress to bradycardia and respiratory depression. Therefore, the combination of absent reflexes and hypotension points to hypermagnesemia. Other disturbances don’t fit this classic pattern as neatly: hyperkalemia causes weakness but reflex loss isn’t a defining feature; hyponatremia presents with CNS symptoms like confusion or seizures; hypocalcemia tends to cause tetany and hyperreflexia rather than absent reflexes.