Les paresthésies apparaissent dans deux cas différents :
Chvostek’s sign: Tapping over the facial nerve as it passes in front of the ear below the zygomatic arch induces muscular spasm (twitching of face, mouth or nose). It is a feature of latent tetany, and may be seen in hypocalcaemia. It can be demonstrated in some patients with normal calcium levels, particularly patients who are anxious.
Trousseau's sign Compression of the arm (eg by a BP cuff on the upper arm inflated a little above the systolic BP) produces carpopedal spasm - 'main d'accoucheur' (obstetrician's hand) with bunching of the fingers and adduction of the thumb. In common with Chvostek's sign it indicates latent tetany and is seen in hypocalcaemia - eg when due to hypoparathyroidism or pseudohypoparathyroidism, Vitamin D or magnesium deficiency, acute pancreatitis, renal failure or alkalosis).
Cf. schémas: http://www3.unil.ch/fbmens/arc/20052006/doc/arc18.pdf