Figure 1
The position that triggered the primary cueing tremor in Case 1. (A) View from the right side of the patient. (B) View from the posterior aspect. Surface electromyographic studies in Case 1 revealed characteristic features of tremor with regular oscillations (C) recording from teres major. Each small square represents a 300-millisecond duration. The spectral peak analysis confirmed a 6.3-Hz frequency in the teres major and infraspinatus muscles (D).
Video 1
This video demonstrates Case 1 and is comprised of Segment 1 and Segment 2, both of which illustrate the same tremor pattern. Segment 2 was recorded with the patient’s upper trunk exposed to better visualize muscle activity. The tremor is best appreciated in the front and back oblique views, where it is more prominent than in the lateral view. The video demonstrates a right arm tremor that occurs specifically when the patient holds the cue in a backward position with an extended right shoulder. The tremor occurs primarily in the internal-external rotation axis, resulting in side-to-side oscillations of the forearm. Of note, the tremor disappears briefly when the patient advances the cue forward to shoot (time mark: 0:40), before reappearing shortly afterward.
Table 1
Literature review of phenomenology and treatments of billiards-related movement disorders compared to the novel cases.
| REFERENCE | SEX | AGE | AGE AT ONSET | DURATION OF PLAYING (YEARS) | PHENO MENOLOGY | AFFECTED BODY REGION | SYMPTOM DESCRIPTION | POSITION SPECIFICITY | ELECTROPHYSIOLOGIC FINDINGS | TREATMENT TRIAL | TREATMENT RESPONSE* |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Case 1 | Male | 55 | 51 | 20 | Tremor | Dominant arm (right) | Tremor when holding a cue backward | Yes, when holding a cue with extension of the right shoulder | Regular oscillations (6.3 Hz) recording from the right teres major and infraspinatus muscles | Propranolol, topiramate, gabapentin, zonisamide, BoNT | Poor to medications; mild-to-moderate to BoNT |
| Case 2 | Male | 66 | 56 | N/A | Tremor | Mainly in non-dominant arm (left), subtle in dominant arm (right) | Tremor when adopting his shooting stance with a pool cue | Yes, when the left hand was acting as the bridge | N/A | Propranolol, topiramate, gabapentin, primidone, clonazepam, TAPS, Vim DBS | Poor to medications and TAPS; moderate to DBS |
| Smilowska et al [10] | Male | 57 | 52 | N/A | Dystonia | Dominant arm (right) | Arm ‘blocked’ when hitting the ball | Yes, when moving the arm back and forth in a pendulum motion, prior to hitting the white cue ball | Co-contraction of right triceps brachii and biceps brachii and excessive activity in the right deltoid and right brachioradial muscles while holding a billiards stick. | BoNT | Excellent |
| Lee et al [7] | Male | 52 | 47 | 30 | Dystonia | Dominant arm (right) | Arm being ‘locked’ when he tried to strike a ball | Yes, when extending the elbow | Co-contraction of triceps and deltoids immediately after bicep contraction when pulling the cue backward | Propranolol, benzodiazepine, anticholinergics, BoNT | Poor |
| Salari et al [9] | Male | 34 | 32 | 22 | “Tremor” | Head | Involuntary neck movements with posture in the position of striking a ball | Yes, when bending his trunk at the hips at approximately 80–90° while supporting his head against gravity by keeping his neck straight | N/A | N/A | N/A |
[i] *Treatment response refers to the outcome reported in each individual patient, as described in the original case report. These descriptors reflect subjective or observed clinical effects and are not intended to imply group-level generalizations. As more cases and objective response measures become available, broader conclusions may be possible.
Abbreviations: BoNT = botulinum toxin; DBS = deep brain stimulation; TAPS = transcutaneous alternating patterned stimulation; Vim, ventral intermediate nucleus of the thalamus, N/A, not applicable.
Table 2
Differentiating between primary cueing tremor from billiards-related dystonia.
| PRIMARY CUEING TREMOR | BILLIARDS-RELATED DYSTONIA | |
|---|---|---|
| Symptoms | Shaking of the arm while cueing | Sudden pause, characterized by “locking” or “freezing” of the dominant arm while cueing; dystonic jerking movements have not been reported |
| Phenomenology | Regular oscillations of the movements | Abnormal posturing while cueing |
| Position specificity | Yes | Yes |
| Involved muscles | Infraspinatus and teres major (in case of tremor in internal-external rotation axis of the arm) | Triceps, biceps, brachioradialis, deltoid |
| Electrophysiology | Regular oscillations with approximately 6-Hz frequency | Co-contraction of agonists and antagonists |
| Alcohol responsivity | Yes | No |
| Response to pharmacological treatment | Poor | Poor |
| Response to botulinum toxin | Varying from poor to mild-to-moderate | Excellent |
| Proposed deep brain stimulation target | Ventral intermediate nucleus (Vim) of the thalamus | Ventralis oralis anterior (Voa) and posterior (Vop) of the thalamus or globus pallidus interna (GPi) |