title: Factor structure and predictive validity of somatic and nonsomatic symptoms from the patient health questionnaire-9: a longitudinal study after spinal cord injury.
abstract: OBJECTIVE
  To investigate the factor structure and predictive validity of somatic and nonsomatic depressive symptoms over the first 2.5 years after spinal cord injury (SCI) using the Patient Health Questionnaire-9 (PHQ-9).
  
  
  METHODS
  Somatic and nonsomatic symptoms were assessed at baseline during inpatient hospitalization (average of 50 days after onset) and during 2 follow-ups (average of 498 and 874 days after onset).
  
  
  METHODS
  Data were collected at a specialty hospital in the Southeastern United States and analyzed at a medical university. We performed time-lag regression between inpatient baseline and follow-up somatic and nonsomatic latent factors of the PHQ-9.
  
  
  METHODS
  Adults with traumatic SCI (N=584) entered the study during inpatient rehabilitation.
  
  
  METHODS
  Not applicable.
  
  
  METHODS
  PHQ-9, a 9-item measure of depressive symptoms.
  
  
  RESULTS
  The inpatient baseline nonsomatic latent factor was significantly predictive of the nonsomatic (r=.40; P=.000) and somatic latent factors at the second follow-up (r=.29; P=.006), whereas the somatic factor at inpatient baseline did not significantly predict either factor. In contrast, when regressing latent factors between the 2 follow-ups, the nonsomatic factor predicted only the nonsomatic factor (r=.66; P=.002), and the somatic factor predicted only future somatic symptoms (r=.66; P=.000). In addition, the factor structure was not stable over time. Item analysis verified the instability of somatic items between inpatient baseline and follow-up and also indicated that self-harm at inpatient baseline was highly predictive of future self-harm.
  
  
  CONCLUSIONS
  Nonsomatic symptoms are better predictors of future depressive symptoms when first assessed during inpatient rehabilitation, whereas somatic symptoms become stable predictors only after inpatient rehabilitation. Self-harm (suicidal ideation) is the most stable symptom over time. Clinicians should routinely assess for suicidal ideation and use nonsomatic symptoms when performing assessments during inpatient rehabilitation.
authors.affiliation: College of Health Professions, Medical University of South Carolina, Charleston, SC, USA. krause@musc.edu
authors.forename: James S
authors.initials: JS
authors.lastname: Krause
authors.forename: Karla S
authors.initials: KS
authors.lastname: Reed
authors.forename: John J
authors.initials: JJ
authors.lastname: McArdle
mesh_terms: D000328:Adult; D003866:Depressive Disorder / Q000175:diagnosis* / Q000209:etiology*; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D026741:Physical Therapy Modalities; D011594:Psychometrics; D012680:Sensitivity and Specificity; D013119:Spinal Cord Injuries / Q000150:complications* / Q000534:rehabilitation; D011795:Surveys and Questionnaires; D013997:Time Factors