Calcium is a critical ion for a number of cellular signaling events. As such, it is not surprising that hypocalcemia leads to a wide variety of signs and symptoms.
The dominant presentation of hypocalcemia is usually neurologic in origin. Individuals with profound hypocalcemia will present with lethargy and altered mental status, and may even present with seizures. More commonly individuals with hypocalcemia will present with numbness or tingling in the perioral and distal fingers and toes which over time will progress to carpopedal spasm, or tetany.
Two named tests of the physical exam--Chvostek's sign & Trousseau's sign--are used to detect neurologic effects of hypocalcemia. In Chvostek's sign, tapping the area over the facial nerve causes an ipsilateral contraction of the facial muscles. While suggestive of hypocalcemia, it can apparently be found in up to 10% of the general population however. In Trousseau's sign, a blood pressure cuff is inflated to slightly above the systolic blood pressure and maintained for over 3 minutes (ouch!). In the presence of hypocalcemia this can lead to carpal spasm and involuntary wrist flexion.
In addition to these neurologic signs & symptoms, hypocalcemia can also have effects on the pulmonary system (wheezing secondary to bronchospasm), cardiovascular system (hypocalcemia is associated with a shortened QTc interval and arrhythmias), and dermatologic findings (chronic hypocalcemia can result in dry skin, brittle nails, and petechiae).