Classification of involuntary movements in dogs: Tremors and twitches

- A tremor is defined as an involuntary, rhythmic, sinusoidal movement of a body part.
- Tremors are divided into resting or action-related.
- Twitches arise from a dysfunction of the peripheral motor nerve.
- Twitches are also known as peripheral nerve hyperexcitability (PNH).
- PNH includes fasciculations, myokymia, neuromyotonia, cramps, tetany and tetanus.

This review focuses on important new findings in the field of involuntary movements (IM) in dogs and illustrates the importance of developing a clear classification tool for diagnosing tremor and twitches. Developments over the last decade have changed our understanding of IM and highlight several caveats in the current tremor classification. Given the ambiguous association between tremor phenomenology and tremor aetiology, a more cautious definition of tremors based on clinical assessment is required. An algorithm for the characterisation of tremors is presented herein. The classification of tremors is based on the distinction between tremors that occur at rest and tremors that are action-related; tremors associated with action are divided into postural or kinetic. Controversial issues are outlined and thus reflect the open questions that are yet to be answered from an evidence base of peer-reviewed published literature. Peripheral nerve hyper-excitability (PNH; cramps and twitches) may manifest as fasciculations, myokymia, neuromyotonia, cramps, tetany and tetanus. It is anticipated that as we learn more about the aetiology and pathogenesis of IMs, future revisions to the classification will be needed. It is therefore the intent of this work to stimulate discussions and thus contribute to the development of IM research.