HIGH AND LOW THRESHOLD FOR STARTLE REACTIVITY ASSOCIATED WITH PTSD SYMPTOMS BUT NOT PTSD RISK: EVIDENCE FROM A PROSPECTIVE STUDY OF ACTIVE DUTY MARINES

Abstract

Background: Heightened startle response is a symptom of PTSD, but evidence for exaggerated startle in PTSD is inconsistent. This prospective study aimed to clarify whether altered startle reactivity represents a trait risk-factor for developing PTSD or a marker of current PTSD symptoms.

Methods: Marines and Navy Corpsmen were assessed before (n = 2,571) and after (n = 1,632) deployments to Iraq or Afghanistan with the Clinician-Administered PTSD Scale (CAPS). A predeployment startle-threshold task was completed with startle probes presented over 80-114 dB[A] levels. Latent class mixture modeling identified three growth classes of startle performance: "high," "low," and "moderate" threshold classes. Zero-inflated negative binomial regression was used to assess relationships between predeployment startle threshold and pre- and postdeployment psychiatric symptoms.

Results: At predeployment, the low-threshold class had higher PTSD symptom scores. Relative to the moderate-threshold class, low-threshold class membership was associated with decreased likelihood of being symptom-free at predeployment, based on CAPS, with particular associations with numbing and hyperarousal subscales, whereas high-threshold class membership was associated with more severe predeployment PTSD symptoms, in particular avoidance. Associations between low-threshold membership and CAPS symptoms were independent from measures of trauma burden, whereas associations between high-threshold membership and CAPS were not. Predeployment startle threshold did not predict postdeployment symptoms.

Conclusions: This study found that both low startle threshold (heightened reactivity) and high startle threshold (blunted reactivity) were associated with greater current PTSD symptomatology, suggesting that startle reactivity is associated with current PTSD rather than a risk marker for developing PTSD.

Keywords: PTSD; anxiety; combat; longitudinal study; prospective study; risk factor; startle.