Definitions

Threshold (VPT, Vibro Perception Threshold); The minimum applied vibration level (intensity) when the patient can sense a vibration in the finger. The Threshold is graded in the unit dB.

Threshold values are recorded as curves at seven different frequencies between 8-500 Hz in a Vibrogram. High Threshold values are positioned low in a Vibrogram, i.e. the y-axis points downwards and high values indicate impaired sensibility

Gray zone; The shaded area at each frequency in a vibrogram, showing corresponding threshold values for healthy persons, i.e. the normal population with the mean value +/- 1 standard deviation.

The area is age-matched meaning that the patients curve is always compared to normal values for a population of the same age. Sensibility is degrading with age, i.e. in analogy with an age-related impairment of the hearing.

Interpretation of a Vibrogram

Sensibility Index, SI, is an easy and useful figure for an overall assessment of the vibrogram curve. As a general rule, a SI > 0.8 should be regarded as normal, while SI < 0.8 indicates pathology.

However, SI is based on a summary of thresholds from all seven frequencies, (8-500 Hz) and sometimes there may be increased vibration thresholds at one or several frequencies, still with the summarized SI being > 0.8.  Therefore, it is important to study the shape of the curve, and to evaluate possible pathology at separate frequencies.  

Usually increased thresholds are first seen at the highest frequencies, i.e. 250 and especially 500 Hz. It is not an unusual finding that the vibration threshold at 125 Hz is normal, while the vibration threshold at 500 Hz can be much increased with a lower position in the vibrogram recording at this special frequency, This can be a sign of early pathology.

Even if SI is normal ( > 0.8) increased thresholds at 250 or/and 500 Hz can motivate  follow-ups at a later stage.

If the patient has cold hands (finger temperature below 27 ´C), this can also result in increased thresholds at 250 and 500 Hz without indicating early pathology.

It is therefore important to consider the temperature and if necessary redo the Vibrametry test if the patient has been too cold. The finger temperature is automatically registered by the VibroSense Meter, but it is possible to perform a vibrametry test even if the temperature is low.  

A vibrogram can be classified as follows (click on the links or vibograms for a large view) :

Stage 0: SI > 0.8, all seven Thresholds (8 – 500 Hz) within the grey zone:
normal  vibrogram (examples  A and  B)

Stage 1: SI > 0.8, One to three Thresholds below the grey zone:
suspected early pathology (example C).

Stage 2: SI< 0.8, low vibrogram curve, just one or a few Thresholds still within the grey zone:
obvious pathology (  example D).

Stage 3: SI<0.8, very low vibrogram curve, all Thresholds under the grey zone:
severe pathology (example  E, right hand)

A complete vibrogram test should include recordings from the index- and little fingers in both hands, i.e. recordings from 4 fingers. The vibration perception in the index- and little fingers reflects function in the median and ulnar nerves respectively.

The summarized result from all four fingers tells a lot about the etiology of a sensory disturbance in the hand(s). Usually a vibration injury results in pathological recordings from all four fingers.

A carpal tunnel syndrome results in a pathological recording from the index finger in the corresponding hand, usually with normal recordings from the other fingers (example F, right hand).

A pathological recording from the little finger may indicate entrapment of the ulnar nerve, usually at elbow or wrist level (example  G, right hand).    

Example A

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Example B

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Example E

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Example F

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Example G