Various types of tremor are differentiated by clinical examination. Characterising the type of tremor makes differential diagnosis easier.
Resting tremor and action tremor are the two main types.
Physiologic tremor occurs in all people, e.g. as static tremor.
Tremor at rest
Occurs in the absence of voluntary movement.
Exhibits low frequency and wide amplitude.
"Pill-rolling" tremor subtype is characterised by minute rolling movements of thumb and forefinger against each other with concomitant small supination-pronation movements of the forearm.
Lower jaw and lips may tremble, but the head hardly ever.
Tremor diminishes or disappears for a moment during movement, e.g. when the arm is lifted to vertical position, but is intensified by mental stress and anxiety.
Tremor at rest or other tremor types do not occur during sleep.
Use of neuroleptics or other dopamine antagonists such as metoclopramide (drug-induced parkinsonism)
Certain extrapyramidal disorders that resemble Parkinson's disease (known as "Parkinson plus" diseases or atypical parkinsonisms)
Essential tremor Essential Tremor may also be associated with tremor at rest although action/postural tremor is clearly more intense.
Action tremor
Manifests only when the muscles are voluntarily contracted, either in active movement or when a fixed position is maintained (static tremor), and disappears when the muscles are relaxed.
Occurs in fingers and upper limbs, but also in head, oral region, larynx (voice) and in lower limbs.
The amplitude of the tremor increases in accurate performance and during stress or anxiety.
Ataxia is an important differential diagnostic sign.
In addition to static or action tremor there may be intention tremor, ataxia, disturbances of equilibrium, nystagmus, speech disturbances and muscular hypotonia.
Tremor is accentuated in distal parts of the body, in upper limbs the frequency is faster than in lower limbs.
Toxic tremor
Especially in heavy metal poisonings tremor in sustained position or action tremor is evident (e.g. mercury, lead, arsenic and phosphorus, but also certain chemicals, such as dioxine).
Carbon monoxide, carbon disulphide, methanol and cyanide poisonings
Myoclonic jerks and other involuntary movements may occur in addition to tremor, and tremor may be present also in rest.
Symptomatic tremor
In many neurological disorders, action tremor may be present in addition to the symptoms of the underlying disease.
Dystonias
Certain neuropathies (e.g. hereditary), polyradiculitis
Brain injuries
Tourette's syndrome
Wilson's and Huntington's disease
Red nucleus tremor (rubral or midbrain tremor)
Orthostatic tremor
Appears in the lower extremities when standing still.
Moving relieves the tremor.
Task-specific tremor
Appears only when performing some specific task, most commonly when writing with a pen.
May be difficult to differentiate from dystonia.
Functional tremor
Often of mixed type (both resting and action tremor) with variable frequency and amplitude
May start suddenly and cease when no attention is paid.
References
Bötzel K, Tronnier V, Gasser T. The differential diagnosis and treatment of tremor. Dtsch Arztebl Int 2014;111(13):225-35; quiz 236. [PubMed]
Fasano A, Deuschl G. Therapeutic advances in tremor. Mov Disord 2015;30(11):1557-65. [PubMed]
Bhatia KP, Bain P, Bajaj N et al. Consensus Statement on the classification of tremors. from the task force on tremor of the International Parkinson and Movement Disorder Society. Mov Disord 2018;33(1):75-87. [PubMed]