Objective Many evidences raise the possibility that this panic disorder (PD) patients with respiratory subtype (RS) may have characteristic structural abnormalities. in RS. Keywords: Cortical thickness, FreeSurfer, Panic disorder, Respiratory type INTRODUCTION Panic disorder (PD) is usually diagnosed when an individual experiences recurrent and spontaneous panic attacks (PAs), which characteristically begin with a sudden unexpected rise of terror associated with many autonomic symptoms, particularly cardiorespiratory symptoms.1 Despite ongoing research, the pathophysiology of this disorder is yet not well understood. According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), PD Apitolisib is usually a unitary diagnostic category.2 Nevertheless, within this category there are diverse clinical presentations, leading to concerns Apitolisib that PD is not a singular diagnosis.3 As a response to these concerns, alternative classification VPREB1 schemes have been devised. Klein4 proposed two PD subtypes: a respiratory subtype (RS) with prominent respiratory symptoms, probably linked to a maladaptive false suffocation alarm system, and the autonomic subtype, with prominent peripheral autonomic symptoms such as palpitations. Other authors have proposed that this subtypes should be defined by the most prominent symptoms during a common PA, such as respiratory, cardiovascular, and gastrointestinal subtypes.5 Briggs et al.6 studied the psychopathology of 1 1,034 PD patients and found a high prevalence of respiratory symptoms. In the first part of that study, the PD symptoms of all patients were analyzed with a principal component analysis, a mathematical procedure similar to factor analysis that transforms a number of possibly correlated variables into a smaller number of uncorrelated variables called principal components. This analysis separated two principal components: the first included eight PD symptoms, whereas the second included a fear of dying, chest pain/discomfort, shortness of breath, paresthesias, and a choking sensation. The first principal component included most of the DSM-IV PD symptoms and was Apitolisib correlated to the severity of PD. The second principal component defined a distinct PD subtype, and the absence of these symptoms defined another subtype. When at least four of the five symptoms from the second principal component were present in a given patient, he or she was considered to fall within the RS group. The RS group suffered more spontaneous PAs and seemed to respond better to antidepressants, whereas patients with a non-respiratory subtype (NRS) had more situational PAs and seemed to respond better to benzodiazepines. In a study by Colasanti and colleagues, mixtures of CO2 were administered to 64 control subjects, and higher concentrations of CO2 produced more stress and PD symptoms.7 The factor analysis extracted three components: the respiratory component was mainly characterized by shortness of breath and choking, but also included dizziness, sweating, and palpitations; the neurovegetative component included trembling, chest pain, chills, nausea, and Apitolisib paresthesias; and cognitive factors included fear of dying, fear of losing Apitolisib control, and derealization. The respiratory component symptoms were correlated with CO2-evoked subjective disturbance, as represented by scores around the electronic Visual Analogue Scale of Anxiety. Accordingly, Nardi et al.8 observed that patients responding to a voluntary hyperventilation challenge in the laboratory also reported more respiratory symptoms during attacks in their daily life, and Biber and Alkin9 found that a respiratory subgroup of patients was more sensitive to the CO2 challenge. Moreover, respiratory subgroups have been shown to have later panic onset, longer illness duration, higher cigarette consumption, and increased agoraphobia.8,9 Because a higher prevalence of asthma occurs in panic patients, this constellation of respiratory symptoms may be linked to this comorbidity. RS patients often have a familial history of PD,10 indicating a potential role of genetic.