RESUMEN
BACKGROUND: Five cases of tremor only upon smiling have been reported where no facial tremor is present at rest, when talking, or with full smile. CASES: This report highlights four cases of tremor upon partial smiling, discusses the phenomenology of smiling tremor, and reviews the current literature. Four subjects with lower facial tremor present only upon smiling underwent movement disorders evaluation with video. Tremor frequencies were determined by parsing the video clips into 1-second intervals and averaging the number of oscillations per interval and were determined to be high-frequency 8 to 10 Hz irregular facial tremors with harmonic variations upon moderate effort in all cases. Slight or full-effort smiling did not elicit facial muscle oscillations. Subjects had no other signs of tremor, dystonia, or parkinsonism on examination or in family history. CONCLUSIONS: Tremor upon smiling only, or isolated smiling tremor, is a unique task- and position-specific tremor of the facial musculature.
