Table 3 Clinical features of organic tremor evaluated and described in studies

Clinical features

A typical feature of PMD is its paroxysmal nature and a sudden onset of the symptoms with no progression [16]

The symptoms are (almost) maximal at or near onset [16]

The tremor can have different directions and change them over time, this can especially be seen in mass loading testing ([2, 16, [20])

Frequency analysis can help to differentiate between organic and functional tremors. Based on a classification of frequency into low (< 4 Hz), medium (4–7 Hz) and high (> 7 Hz) tremors with frequency > 11 is usually organic, but there is no rule with lower frequencies. Essential tremor is often 6 or 7 Hz, many tremor frequencies were suggested between 6 and 11 Hz to be often functional ([1, 2, 16, 20])

The amplitude, frequency as well as direction show a higher variability in functional tremor than in organic forms, usually the frequency of organic tremor does not show a variation higher than 0.5 to 1.0 Hz, in functional tremor a larger variation in frequency may be observed ([1, 2, 16, 20])

Tremor shows different reactions to distraction and can cease or vary in intensity or frequency ([16, 20])

In an entrainment test, the tremor takes up the frequency of a tapping in an unaffected extremity e.g. finger tapping ([16, 20])

Often functional tremor can be precipitated by suggestion [16]

Impaired walking and standing without a tendency to fall is often detected in functional tremor, meaning swaying gait and apparent balance problems without falling [16]