Age of Onset: Can We Rely on Essential Tremor Patients to Report This? Data from a Prospective, Longitudinal Study

BACKGROUND: Essential tremor (ET) is among the most prevalent neurological diseases. Age of onset, a key variable in neuroepidemiological and genetic research, is chiefly assessed by self-report rather than medical record review; the latter may be of little use. As a researcher, one wonders about the quality of this self-report. Is age of onset something which can be reproducibly self-reported by patients? There are few published data to aid researchers. METHODS: Age of onset was self-reported at two time points (baseline and follow-up) in 86 ET cases in a longitudinal epidemiological study in New York. RESULTS: The mean follow-up interval was 5.7 ± 2.5 (maximum = 14) years. Overall, agreement between the baseline and follow-up reports was high (ρ = 0.85, p < 0.001). Yet the difference (age of onset (baseline) - age of onset (follow-up)) ranged widely (from -47 to 32 years), and in one fifth of cases was ≥ 10 years. Greater agreement was associated with several clinical factors including age, medication use, embarrassment, depressive symptoms, cognitive test score and disease duration. CONCLUSIONS: Differences in reported age of onset in ET may vary widely, and in up to one fifth of patients may be substantial. Investigators should approach these self-reports with caution.