Signs of Latent Tetany
                   1.            Chvostek's sign
                   2.            Trousseau's sign
                   3.            Hyperventilation test
                   4.            Trousseau-von Bonsdorff Test
                   5.            Pool-Schlesinger sign
                   6.            Peroneal sign
                   7.            Erb's sign
                   8.            Escherich's sign

1.       Chvostek's sign
(František Chvostek -1835-1884, Austria)
Elicitation:
n Elicited by tapping the facial nerve-
n  either just anterior to the earlobe and below the zygomatic arch (Chvostek I phenomenon),  or
n  Between the zygomatic arch and the corner of the mouth (Chvostek II phenomenon).
               Response:
n   A positive response varies from twitching of the lip at the corner of the mouth to spasm of all facial muscles, depending on the severity of hypocalcemia.
Advantages:
n  It precedes other signs of hypocalcemia and persists until the onset of tetany.
n  Convenient bed side examination.
              Limitations:
n  Crude indicator of neuro-muscular irritability and an unreliable indicator of hypocalcemia.
n  High incidence of false +ve (25%) & false –ve (29%) responses.
n  Can’t be elicited during tetany because of strong muscle contractions.
n  May also be +ve in rickets, diphtheria, measles, scarlet fever, whooping cough, and myxedema.
n  May be +ve in healthy infants, so can’t be used for neonatal tetany.

2.       Trousseau's sign
 (Armand Trousseau, 1801-1867, France)
Elicitation:
n  Apply a blood pressure cuff to the patient's arm; then inflate the cuff to a pressure between the patient's diastolic and systolic readings, and maintain it for 4 minutes.
Response:
n  Carpal spasm (main d’accoucheur or obstetrician hand)
n  paresthesia of the fingers,
n   muscular fasciculations or twitches of the fingers, and
n  A sensation of muscular cramping or stiffness.
Advantages:
n  Both sensitive and specific for hypocalcemic tetany.
n  Rarely +ve in normal subjects.
               Limitations:
n  sometimes positive in hysterical subjects or,
n  in workers whose hands are held in a semi-tetanic position for some hours daily-e.g., seamstresses, cobblers, and glove or leather stitchers.
n  Rarely its +ve only in dominant arm.

3.       Hyperventillation test
Elicitation:
n  Hyperventilate at the rate of 55-60/min for 3 min. sitting upright, with the hands placed loosely on the knees.
Response:
n  If no tetanic manifestation develops, tetany is ruled out.
Advantage:
n  High specificity (9/72 normal dev. carpel cramps after 3 min.)
Disadvantage:
n  Disturbing generalized signs and symptoms after hyperventilation for two or more minutes.
n  Usually it is also found positive only when the tourniquet test is already positive, therefore no further information is gained. (7/64 hypocalcaemic gave +ve test when Tourniquet test was –ve).
n  Failure in cases which restrict proper movement of diaphragm (asthma, emphysema, recurrent laryngeal nerve injury, abdominal tumors, pregnancy)
n  Serious physical or mental disability.
n  Children under 10 years of age.

4.       Trousseau-von Bonsdorff Test
(combined Tourniquet + Hyperventillation test)
Elicitation:
n  sitting upright, with the hands placed loosely on the knees
n  Tourniquet applied for 4 min.
n  If no definite carpel cramp appear, tourniquet is removed and subject is asked to hyperventilate at the rate of 40 breaths/min.
n  Test is stopped at 75 sec or sooner if carpel cramp appears.
Response:
n  The hand previously under the tourniquet becomes spastic before 75 seconds, with few or no generalized symptoms of tetany.
n  Rarely the opposite hand can become cramped also, but not so intensively.
Advantage:
n  It shows that tetany is often a summation of factors which increase the sensitivity of the nervous system. (alkalosis + hperexcitability)
n  Reduces the period of hyperventilation, eliminates the possibility of an unpleasant generalized tetany.
n  It also reduces the frequency of hyperventillation.
n  More sensitive than either the tourniquet test or the hyperventilation test alone.
               Disadvantage:
n  Failure in cases which restrict proper movement of diaphragm (asthma, emphysema, recurrent laryngeal nerve injury, abdominal tumors, pregnancy)
n  Serious physical or mental disability.
n  Children under 10 years of age.

5.       Pool-Schlesinger sign
Elicitation:
n  Forcefully abduct and elevate the patient's arm with his forearm extended. (Pool’s phenomenon/arm phenomenon)
n  Forcefully flex the patient's extended leg at the hip. (Schlesinger's sign/leg phenomenon)
Response:
n  Muscle spasm of the forearm, hand, and fingers or of the leg and foot.
n  Spasm results from tension on the brachial plexus or the sciatic nerve.

6.       Peroneal sign
Elicitation:
n  Tap over the common peroneal nerve (lateral neck of the fibula with the patient's knee relaxed and slightly flexed). 
 Response:
n  Dorsiflexion and abduction of the foot.

7.       Erb’s sign:
n  Increased irritability of motor nerves, detected by electromyography.

8.       Escherich's sign:
n Contraction of the lips, tongue, and masseters on percussion of the inner surface of the lips or the tongue.