“Weight‐holding tremor”: An unusual task‐specific form of essential tremor?

To the Editor: Patients with a variety of tremors often note certain activities that specifically accentuate the abnormal movements. Some patients have tremor only on the performance of specific tasks. We describe an interesting patient with presumed essential tremor who noted that his tremor was almost exclusively brought out by carrying a weight in his hands. This 76-year-old retired school administrator gave a 5-year history of tremor. The tremor involved both hands and first became evident when he was carrying a bag of groceries home from the store. Initially the problem was intermittent, but it gradually became present whenever he held any weight in his hand. The heavier the weight, the more pronounced the tremor became. The tremor improved if he lifted up his arm while weighted or performed some other purposeful action with it. The tremor might also occur while eating soup with a spoon. Typically, if he held the hand midway between the bowl and his mouth, tremor would occur and sometimes cause spillage, but it would completely subside as he reached his mouth. A tremor was rarely evident with the hands at rest, and occasionally his wife would become aware of tremor while holding his hand. The tremor did not impair writing or fine motor tasks. He had also noticed a mild head tremor, which had been slowly progressive since the onset of the hand tremor. He had noted no aggravating or relieving factors for the tremor including alcohol. There were no other neurological symptoms. His mother had an action tremor of her hands beginning in her 70s, and a maternal uncle had both hand and head tremors. On examination, he had a slight head tilt with chin up and to the left with slight contraction of the right trapezius. There was a low amplitude rapid “no-no” tremor of the head at rest. This was diminished by conscious effort. He had a very intermittent low amplitude tremor at rest in the right wrist with the arm extended by his side but not while walking. The tremor greatly increased when he held a weighted bag by his side. Removal of the weights from the bag caused the tremor to subside. A similar but less prominent tremor existed in the left wrist. There was no postural tremor in the outstretched hands, and only a slight end-point tremor of the left hand on finger-to-nose testing. Tone, power, and coordination, including the performance of rapid repetitive and alternating movements, were normal. The tremor could not be induced in the lower extremities with successively increasing weights. Gait was normal with normal arm swing and excellent postural stability. He had no primitive reflexes including excessive blink to glabellar tap (i.e., Myerson’s sign). The remainder of the neurological examination was unremarkable. Writing was large, with no sign of tremor in script or drawing. The tremor was recorded with surface electrodes over the right forearm flexor and extensor muscles and with an accelerometer over the dorsum of the hand. Reflex activity of the forearm flexor and extensor muscles in response to finger taps and to stimulation of the digital nerves of the ring finer was recorded by averaging rectified voluntary electromyographic (EMG) activity from these muscles during repeated stimulation (1). An alternating 5-Hz tremor with EMG bursts <100-ms duration in flexors and extensors occurred when he held a weighted bag in the fingers (Fig. 1B). The tremor was quite dependent on tension in the forearm muscles, and the tremor disappeared completely when the weight was removed (Fig. 1Aj. There was no exaggeration of the short or long latency reflex responses to finger taps or to electrical stimulation of digital nerves at twice perception threshold. This patient’s tremor was particularly brought out by holding weight in the upper limbs with the arms relaxed and extended at the sides. One can only speculate on the proper classification of this movement disorder as either a distinct action-specific tremor, a variant of essential tremor, or parkinsonism. As the tremor was brought out by a specific action such as weight bearing, it may be akin to other action-specific tremors. Such tremors, with or without concomitant dystonia, have been described while performing specific tasks such as writing, golfing, typing, drinking, and playing piano (2). Our patient may have had mild cervical dystonia, but the head tremor was more in keeping with essential tremor than with dystonic tremor. There was no dystonic posturing of the extremities. The family history was also more compatible with essential tremor, although it is recognized that isolated tremor may be a forme fruste of idiopathic dystonia in some members of well-documented dystonia pedigrees. The effect of limb position and eIectrica1 stimulation on tremor has been studied by numerous investigators. In one study ( 3 ) , essential tremor was not significantly affected by limb position in contrast to cerebellar, parkinsonian, and other tremors that showed postural dependence. This observation was used to classify patients into essential versus more pathological tremors. In the present case, electrophysiological assessment suggested that other than weight bearing, external perturbations such as limb position or electrical stimulation had little influence on forearm muscle activity. Several previous studies have suggested that tremor can be reset by brief peripheral mechanical and electrical perturbations (43) . Despite the belief that essential tremor may be more dependent on peripheral afferent input than parkinsonian tremor, such maneuvers have generally failed to distinguish between them. Although the frequency of the tremor in our case was similar to the rest tremor of Parkinson’s disease (PD) and although some PD patients, especially early in the illness, note that their tremor is brought out in certain positions or with