title: Diaphragmatic height index: new diagnostic test for phrenic nerve dysfunction.
abstract: OBJECTIVE
  The diaphragmatic height index (DHI) was developed to measure the difference in diaphragm levels. The purpose of this study was to set definite DHI values and test the accuracy of these values for use as a new diagnostic test for phrenic nerve dysfunction.
  
  
  METHODS
  All data for this study were obtained from medical charts and retrospectively reviewed.
  
  
  RESULTS
  One hundred sixty-five patients with brachial plexus injury who had undergone nerve transfers between 2005 and 2008 were divided into Groups A and B. Group A consisted of 40 patients (mean age 28.0 years) who had sustained concomitant injury of the brachial plexus and phrenic nerves. Patients in Group A1 had right phrenic nerve injury and those in Group A2 had left phrenic nerve injury. Intraoperative direct electrical stimulation of the phrenic nerve was considered the gold standard in assessing nerve function in all patients with brachial plexus injury. Group B consisted of 125 patients (mean age 28.7 years) with brachial plexus injury and normal phrenic nerve function. Group C, the control group, consisted of 80 patients with nonbrachial plexus injury (mean age 34.0 years) who had undergone other kinds of orthopedic operations between April and June 2009. Standard posteroanterior chest radiographs were blindly interpreted using the Siriraj inhouse picture archiving and communication system in all 245 patients in the study. First, a reference line (R line) was drawn along the inferior endplate of T-10. Then, 2 lines (lines A and B) were drawn through the highest point of each diaphragm and parallel to the R line. The difference between these 2 lines divided by the height of T-10 was defined as the DHI. The cutoff points of the DHI for diagnosing right and left phrenic nerve dysfunction were analyzed with a receiver operating characteristic curve. The accuracy of these DHI values was then evaluated. The DHI in Group C was 0.64 ± 0.44, slightly higher than the DHI in Group B, with no significant difference. Diaphragmatic height indexes in Groups A1 and A2 were 2.0 ± 0.99 and -1.04 ± 0.83, respectively, which were significantly different from those in Groups B and C (p < 0.05). The cutoff point of the DHI for diagnosing right phrenic nerve dysfunction was > 1.1, and that for left phrenic nerve dysfunction was < 0.2. The sensitivity and specificity of right and left DHI values were 90.5% and 86.3%, and 94.7 and 88.3%, respectively.
  
  
  CONCLUSIONS
  Data in this study show that diaphragm paralysis can be simply and reliably predicted by the DHI. Diaphragmatic height index values > 1.1 and < 0.2 are proposed as the new diagnostic test for right and left phrenic nerve dysfunction with a high degree of accuracy. This index is applicable in diagnosing phrenic nerve dysfunction that occurs concomitantly with brachial plexus injury or from other etiologies.
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand.
authors.forename: Chaturong
authors.initials: C
authors.lastname: Pornrattanamaneewong
authors.forename: Roongsak
authors.initials: R
authors.lastname: Limthongthang
authors.forename: Torpon
authors.initials: T
authors.lastname: Vathana
authors.forename: Kamolporn
authors.initials: K
authors.lastname: Kaewpornsawan
authors.forename: Panupan
authors.initials: P
authors.lastname: Songcharoen
authors.forename: Saichol
authors.initials: S
authors.lastname: Wongtrakul
mesh_terms: D000293:Adolescent; D000328:Adult; D001134:Arm Injuries / Q000473:pathology; D001917:Brachial Plexus / Q000293:injuries; D020516:Brachial Plexus Neuropathies / Q000175:diagnosis / Q000000981:diagnostic imaging; D003627:Data Interpretation, Statistical; D003964:Diaphragm / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000294:innervation; D004558:Electric Stimulation; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008297:Male; D008875:Middle Aged; D009417:Nerve Tissue / Q000637:transplantation; D010523:Peripheral Nervous System Diseases / Q000175:diagnosis* / Q000000981:diagnostic imaging; D010791:Phrenic Nerve / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D012372:ROC Curve; D013902:Radiography, Thoracic; D015203:Reproducibility of Results; D012189:Retrospective Studies; D055815:Young Adult