Fifteen years after 9/11, a new Yale study may help scientists develop treatments for first responders suffering from post-traumatic stress disorder.

Researchers from Yale and the Icahn Mount Sinai Institute collaborated on an study that identified three kinds of PTSD acquired by first responders at the World Trade Center. The more nuanced picture provided by this analysis can help improve treatment options for victims of PTSD, according to Adriana Feder, lead researcher on the study and an associate professor of psychiatry at the Icahn School of Medicine at Mount Sinai.

“There are various forms of therapeutic strategies that are also similarly tailored to different PTSD symptom profiles,” Feder said. “So really [the purpose of this study] was to give us a more nuanced understanding of the predominant expression of this same disorder. Everyone [in this study] has PTSD, [but] it’s manifesting in different ways.”

The study’s researchers took advantage of an unusually large sample of 4,352 World Trade Center responders drawn from a larger cohort of the over 32,000 first responders who attended the World Trade Center Health Program, a regional clinical consortium established by the Centers for Disease Control and Prevention in 2002. The program comprises five medical institutions in the greater New York City area that provide health monitoring and treatment services for police and other World Trade Center responders, according to the study.

The researchers applied a technique called “latent class analysis,” an analytical approach that enabled them to identify subgroups within a larger sample that clustered together on the basis of PTSD symptoms. This technique allowed researchers to identify three subtypes of PTSD among the responders participating in the study, according to Robert Pietrzak, a lead researcher on the study and an associate professor at the Yale School of Medicine.

The first subtype of PTSD, “high symptom,” was found in 45.3 percent of study participants, who displayed all the typical hallmarks of PTSD symptoms. The second subtype, “dysphoric,” was present in 31 percent of all participants, who were characterized by high probabilities for debilitating symptoms like sleep disturbance and emotional numbing. The third group, “threat,” manifested itself in 23.2 percent of the responders, who exhibited high probabilities for recurring intrusive thoughts about trauma.

Understanding the symptoms of different manifestations of PTSD is crucial to providing proper treatment for the first responders, Pietrzak said. For example, since individuals who fall into the “dysphoric” category of PTSD presentation exhibit more depressive symptoms than “threat” symptoms like intrusive thoughts of trauma, they might benefit more from treatments that specifically focus on emotional numbing and other symptoms of depression, according to Pietrzak.

The study uncovered many of the subtle differences that exist between different subtypes of PTSD and the possible causes for its different manifestations across various first responders. For example, the group within the “threat” category of PTSD had a higher number of WTC exposures compared to the other two. They were more likely to have handled human remains, worked longer than the median number of hours at the site and been caught in the dust cloud after the towers fell. Likewise, the responders in the “high symptom” class of PTSD were more likely to have known someone injured on 9/11 than those in the “threat” class.

“What all this might mean is that these sort of traumatic exposures may be uniquely related to the manifestation of PTSD in this population,” Pietrzak said.

John Krystal, the chair of the medical school’s department of psychiatry, said the study provided additional important lessons. He said that the research revealed that trauma, anxious arousal and avoidance are not necessarily the essential markers of PTSD that they are commonly thought to be, as roughly one third of the study’s PTSD patients did not display these symptoms. Besides that, the study found that “high symptom” PTSD patients had the highest probability of suffering from depression.

According to Krystal, since symptoms of depression may not always be effectively mitigated by typical antidepressant treatment of PTSD, new forms of treatment may need to be developed to successfully treat these patients. He added that the study’s findings have important implications for the future of PTSD research.

“It is clear that there are distinct patterns of PTSD and that we do not understand very much about the biology and course of these types of PTSD,” Krystal said. “A better understanding of the subtypes of PTSD may help us to develop more focused and therefore more effective treatments for each subtype of this disorder.”

Feder and Pietrzak are already at work on several ongoing studies that build on the findings of this one, according to Feder. One of these studies will examine biological markers of PTSD and will investigate whether the latent PTSD classifications identified in the study are differentially linked to those markers. They are also writing a grant for a study of WTC responders employing functional neuroimaging to identify neural networks that might be involved in bolstering psychological resilience. The ultimate goal of this research is to develop more personalized treatments not just for WTC responders but for disaster responders in general.

In total, 411 emergency workers were killed while responding to the 9/11 attacks.