Provocative tests
There is a long history of provocative clinical tests for CTS. By this term we mean physical manoeuvers which can be carried out in the clinic with little or no equipment with the aim of temporarily increasing the carpal tunnel pressure and provoking symptoms. The oldest and still the best of these is Phalen’s test but details of all the ones I know of are given below. These tests should be treated like any other medical investigation - they all generate some false positive results (abnormal test results in subjects who do not have CTS) and some false negative results (normal test results in subjects with CTS). Furthermore, if one carries out all of them aggressively in any given individual there is a high risk that at least one of them will produce a false positive.
PHALEN’S TEST - originally devised by George Phalen who published the first large series of operations for CTS (Phalen 1966). The essence of the test is that the wrist is flexed for one minute while the patient is asked to report whether their usual symptoms are precipitated. The test can be partially quantified by recording the time taken for symptoms to appear. People have devised several ways of positioning the patient to achieve the necessary wrist flexion but it is best to stick to the method originally described by Phalen.
The forearm is held vertically and the wrist is allowed to drop into 90 degrees of flexion under the influence of gravity. If stiffness of the wrist does not permit 90 degrees of flexion then the wrist should be allowed to fall as far as possible. Forced flexion, by the examiner grabbing the hand and deliberately bending it, or by asking the patient to press the backs of the hands together in front of them, should be avoided as this increases the number of false positive tests. An important element of the test is that it is only positive if the symptoms elicited are essentially the same as those of which the patient is complaining to begin with. This test is simple enough to be done at home by the patient and is entirely safe if done as described. If you want to try it you can report the result to us here if you register. You can make the test semi-quantitative by measuring how long it takes for symptoms to appear. When compared against other ways of confirming the diagnosis Phalen’s test is positive in about 70% of cases and has a false positive rate of about 30%.
REVERSE PHALEN’S TEST - The traditional Phalen’s test works because wrist flexion elevates the carpal tunnel pressure. Pressure measurements in the carpal tunnel confirm that this is the case, both in normal individuals and those with CTS but also that bending the wrist in the opposite direction (the movement known as extension) increases the carpal tunnel pressure too and to a rather similar extent. One can thus perform a similar test by extending the wrist to 90 degrees. This version has been less studied than Phalen’s test but is probably slightly less sensitive.
TINEL’S SIGN - Jules Tinel studied wartime nerve injuries in France. He observed that, after a laceration to a nerve one could track the process of regrowth by tapping (percussion) over the course of the nerve. A cut to a nerve results in a recovery process much like that one sees after pollarding a tree. The remaining stump of nerve sprouts many new nerve fibres which grow out in all directions from the injury site. Some of them will grow along the old course of the injured nerve and with luck will eventually re-connect to the original target tissues of that nerve. These newly regenerating nerve fibres are mechanically sensitive at their growing tips and light percussion directly over them triggers nerve impulses which are felt by the patient as a tingling or pins and needles sensation (the original French word is ‘fourmillement’ for which the closest English equivalent might be ‘formication’ - the sensation of ants crawling on the skin). This sensation is felt not at the site which the examiner is tapping, but in the area of the body to which the nerve was connected before it was injured. The site at which tapping elicits the sensation is then indicative of the point which regenerating fibres have reached and can be tracked down a limb as recovery progresses. Who first thought of applying this to carpal tunnel syndrome is not certain nor is the logic behind it entirely obvious as there are usually no mechanically sensitive regenerating nerve fibres in CTS - at least not in early cases. Nevertheless, if percussion over the wrist elicits tingling in the fingers this is widely believed to be a positive Tinel sign for CTS. It is hard to standardise this test. Some examiners use their own fingers to tap the wrist, others use a tendon hammer, and the exact site percussed may be over the carpal tunnel or may be proximal to it. Comparisons with other methods of making the diagnosis suggest that Tinel’s sign may be very unreliable in CTS with anything up to 50% false positive and false negative rates - essentially no better than tossing a coin.
DURKAN’S CARPAL COMPRESSION TEST - this relies upon direct pressure applied externally by the examiner over the carpal tunnel to increase the pressure. It can performed by pressing with the examiners thumbs (Durkan 1991) or with a device designed to apply a standard amount of pressure (Durkan 1994). The former method is difficult to standardise, the latter requires the instrument thus limiting its easy applicability in the ordinary clinic. Neither version has been extensively evaluated against other ways of confirming the diagnosis.
TOURNIQUET TEST- One of the earlier suggestions for temporarily increasing rhe carpal tunnel pressure was to apply a blood pressure cuff to either the upper arm or forearm, inflated to between systolic and diastolic pressure. This obstructs venous return from the arm and the resulting increased blood volume in the hand increases the tunnel pressure. This is one of the less reliable tests.
HAND ELEVATION TEST (Ahn 2001) - The hands are held above the head for two minutes and if this produces the same symptoms of which the patient is complaining then the test is positive. This was originally reported to show 75% sensitivity and 98% specificity for CTS when evaluated in 200 CTS and 200 control hands but has not been as widely studied as some of the other tests described here.
FLICK SIGN - (Pryse-Phillips 1984) - Not strictly a provocative test, this refers to asking the patient what they do with hand at night when they experience symptoms. If the patient demonstrates a ‘shaking out’ movement of flicking the wrists then the sign is positive. Originally claimed to show 93% sensitivity and 95% specificity for CTS, subsequent investigators have found it performs less well.
Revision date - 11th June 2011
