Assessing tremor to rule out psychogenic origin: It’s tricky

Tremors are a rhythmic and oscillatory movement of a body part with a rela­tively constant frequency.¹ Several subtypes of tremors are classified on the basis of whether they occur during static or kinetic body positioning. Assessing tremors to rule out psychogenic origin is one of the trickiest tasks for a psychiatrist (Table 1²). Non-organic movement disor­ders are not rare, and all common organic movement disorders can be mimicked by non-organic presentations.

Diagnostic approach
Start by categorizing the tremor based on its activation condition (at rest, kinetic or inten­tional, postural or isometric), topographic distribution, and frequency. Observe the patient sitting in a chair with his hands on his lap for resting tremor. Postural or kinetic tremors can be assessed by stretching the arms and performing a finger-to-nose test. A resting tremor can indicate parkinsonism; intention tremor may indicate a cerebellar lesion. A psychogenic tremor can occur at rest or during postural or active movement, and often will occur in all 3 situations (Table 2).^1-3

Some of the maneuvers listed in Table 3 are helpful to distinguish a psycho­genic from an organic cause. The key is to look for variability in direction, amplitude, and frequency. Psychogenic tremor often increases when the limb is examined and reduces upon distraction, and also might be exacerbated with movement of other limbs. Patients with psychogenic tremor often have other “non-organic” neurologic signs, such as give-way weakness, deliber­ate slowness carrying out requested vol­untary movement, and sensory signs that contradict neuroanatomical principles.

Investigation
Proceed as follows:

1. Perform laboratory testing: thyroid func­tion panel and serum copper and cerulo­plasmin levels.²

2. Perform surface electromyography to differentiate Parkinson’s disease and benign tremor disorders.²

3. Obtain a MRI to assess atypical tremor; findings might reveal Wilson’s disease (basal ganglia and brainstem involvement) or fragile X-associated tremor/ataxia syndrome (pontocerebel­lar hypoplasia or cerebral white matter involvement).³

4. Consider dopaminergic functional imaging scanning. When positive, the scan can reveal symptoms of parkinson­ism; negative findings can help consoli­date a diagnosis of psychogenic tremor.³

Disclosures
The authors report no financial relationships with any company whose products are mentioned in this article or with manufacturers of competing products.