Alprazolam reduces response to loud tones in panic disorder but not in posttraumatic stress disorder

Background: Posttraumatic stress disorder (PTSD) and panic disorder (PD) share several clinical features, and theory postulates that phasic arousal is similarly dysregulated in both. The modulation of phasic arousal can be probed by measuring the effect of pharmacologic agents on auditory startle. Methods: Eyeblink electromyogram, heart rate, and skin conductance (SC) responses to 15 consecutive presentations of 1000-Hz, 95-dB, zero rise-time pure tones were measured, before and during treatment with alprazolam, in 9 PTSD and 9 PD patients. Concurrent anxiety was assessed by the Hamilton Anxiety Rating Scale. Results: The groups did not differ in initial psychometric and physiological measures. Significant decrease in anxiety was observed in both groups during treatment. A decrease in response probability and a decrease in the SC responses were observed in PD, but not in PTSD. Conclusions: The results may reflect a difference in the modulation of phasic arousal between the disorders. They may also express an impaired between-session habituation or contextual sensitization in PTSD.