Characteristics of fatigue in panic disorder patients

Authors


*Mamoru Tochigi,MD, PhD, Department of Neuropsychiatry, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8655, Japan. Email: mtoc-tky@umin.ac.jp

Abstract

It was suggested that fatigue is one of characteristics of panic disorder. Fatigue was assessed in 360 patients with panic disorder using the Japanese version of the Multidimensional Fatigue Inventory (MFI-J). The scores for general fatigue and reduced activity were significantly higher in the patients than in the controls. These tendencies were also observed in men when the subject group was differentiated according to sex, but not in women. In contrast, the trend for higher score for physical fatigue was observed only in the female patients. Thus, the present study suggests that the characteristics of fatigue vary with sex in panic disorder.

PANIC DISORDER IS one of the anxiety disorders and it is characterized by the spontaneous, unexpected occurrence of panic attacks, accompanied by various somatic and cognitive symptoms. Several studies have suggested an association between panic disorder and fatigue. Manu et al. observed a 10-fold higher prevalence of panic disorder in subjects with chronic fatigue than in a general population.1 Walker et al. also observed that subjects with fatigue were significantly more likely to have experienced current and lifetime episodes of panic disorder.2 In the Katerndahl study, fatigue severity correlated with severity of phobic anxiety in panic attack patients.3 Thus, it was suggested that fatigue is one of the characteristics of panic disorder. But few studies have investigated the characteristics of fatigue in patients with panic disorder. In the present study we assessed fatigue in patients with panic disorder using the Japanese version of the Multidimensional Fatigue Inventory (MFI-J), a 20-item questionnaire for the assessment of fatigue, based on a five-factor model: general fatigue, physical fatigue, mental fatigue, reduced motivation, and reduced activity.4 The three dimensions of fatigue, general, physical, and mental fatigue were labeled based on the manners in which fatigue can be expressed. General fatigue can be expressed by general remarks concerning functioning. Physical fatigue refers to physical sensations, related to the feeling of tiredness. Mental fatigue refers to cognitive symptoms, such as having difficulty in concentrating. Reduced motivation corresponds to a lack of motivation to start any activity, and reduced activity, a frequently occurring reduction in activity, although not necessarily the consequence of fatigue.4

METHODS

Subjects consisted of 360 Japanese patients with panic disorder (113 men, 247 women; mean age, 36.3 ± 9.6 years), recruited from outpatients of Akasaka Mental Clinic, located in Tokyo. All patients met the DSM-IV criteria for panic disorder, 199 of which also had agoraphobia. Although none of them met the DSM-IV criteria for any mood disorders, the Self-rating Depression Scale–Japanese Version (SDS-J) was completed in order to measure subdiagnostic depressive symptomatology.5 One of the authors repeatedly interviewed patients in order to confirm diagnosis. Age of onset and duration of illness were 27.9 ± 9.5 years and 8.3 ± 7.1 years, respectively. History of major physical illness was excluded. Controls consisted of 1004 volunteers from a general Japanese population (809 men, 195 women; age, 37.7 ± 9.1 years), residing in the same area of Japan. They were mainly recruited from the staff of private pharmaceutical companies. The subjects filled out the Japanese version of the MFI, the validity and reliability of which have already been confirmed in a Japanese population. The SDS-J was also completed by the controls. The objective of the present study was clearly explained and written informed consent was obtained from all subjects. The study was approved by the Ethics Committee of Akasaka Mental Clinic.

The analysis of covariance (ancova) was used to compare the MFI-J scores between the patients and controls. The sex, age, and SDS-J score of the subjects were included as covariates, if their effects were significant. The comparison was also conducted after dividing the subjects according to sex. To examine the effect of subdiagnostic depressive state for the MFI-J scores, two analyses were conducted: Pearson correlation was done for scores for the MFI-J factors and the SDS-J; and the second analysis was a comparison of the scores for the MFI-J factors between the patients with SDS-J score <55 and >56 on the basis of the severe cut-off score6 (Student's t-test). SPSS for Windows (SPSS, Chicago, IL, USA) was used for all analyses.

RESULTS

Table 1 summarizes the comparison of the scores for the MFI-J factors between panic disorder patients and controls. The scores for general fatigue, physical fatigue, and reduced activity were significantly higher in the patients than in the controls (= 7.89, P = 0.005; F = 4.26, P = 0.039; and F = 7.20, P = 0.007, respectively, ancova, uncorrected). In men the scores for general fatigue, mental fatigue, and reduced activity were significantly higher in the patients than in the controls (= 8.87, P = 0.003; F = 4.66, P = 0.031; and F = 6.40, P = 0.012, respectively, ancova, uncorrected). In women the score for physical fatigue was significantly higher in the patients than in the controls (= 4.07, P = 0.044, ancova, uncorrected). The differences in the scores for general fatigue in the total and male subjects and reduced activity in the total subjects were still significant after correction for five MFI-J factors (= 0.025, 0.015 and 0.035, respectively). No other significant difference in the scores for the MFI-J factors was observed in this comparison.

Table 1.  MFI-J factors (mean ± SD)
 nSDS-JMFI-J factors
General fatiguePhysical fatigueMental fatigueReduced motivationReduced activity
  1. MFI-J scores were compared using analysis of covariance (ancova). Sex, age, and SDS-J score of the subjects were included as covariates if their effects were significant.

  2. MFI-J, Japanese Version of the Multidimensional Fatigue Inventory; SDS-J, Self-rating Depression Scale – Japanese Version.

Total
 Panic disorder patients36041.1 ± 10.713.5 ± 3.612.6 ± 4.111.3 ± 3.99.9 ± 3.610.3 ± 4.0
 Controls100434.9 ± 8.612.8 ± 3.610.7 ± 3.410.6 ± 3.18.9 ± 2.78.6 ± 2.5
 F 7.894.262.380.7507.20
 P 0.0050.0390.120.390.007
Male
 Panic disorder patients11337.9 ± 10.012.9 ± 3.711.8 ± 3.910.8 ± 3.69.4 ± 3.39.8 ± 3.6
 Controls80934.3 ± 8.412.7 ± 3.610.6 ± 3.410.6 ± 3.08.8 ± 2.78.6 ± 2.5
 F 8.871.914.660.1896.40
 P 0.0030.170.0310.660.012
Female
 Panic disorder patients24742.6 ± 10.813.7 ± 3.513.0 ± 4.111.5 ± 4.110.2 ± 3.710.5 ± 4.7
 Controls19537.6 ± 8.613.0 ± 3.411.1 ± 3.410.4 ± 3.49.0 ± 2.99.0 ± 2.6
 F 2.464.070.1600.5871.21
 P 0.120.0440.690.440.27

DISCUSSION

In the present study we explored the characteristics of fatigue in panic disorder patients using the MFI-J. The scores for MFI-J were compared between patients and controls. The scores for general fatigue and reduced activity were significantly higher in the patients than in the controls (= 0.025 and 0.035, corrected). These tendencies were also observed in men when the subject group was differentiated according to sex, but not in women. In contrast, the trend for higher score for physical fatigue in the total patients was observed in women after differentiation according to sex, but not in men. The weak tendency of higher score for mental fatigue was observed in the male patients, although it was not observed in the total patients. Thus, the present study suggests that the characteristics of fatigue vary with sex in panic disorder; they are relatively prominent in mental aspect and activity for male patients, and in the physical aspect for female patients.

There has been no study that investigated the characteristics of fatigue in panic disorder or major depressive disorder, to our knowledge, although several studies investigated the relationship between MFI factors and anxiety or depression in patients with Parkinson's disease or cancer.7–9 All studies observed that depression correlated with all dimensions of the MFI factors except for physical fatigue in the patients with Parkinson's disease in the Lou et al. study.7 With respect to anxiety, Munch et al. observed significant correlation with general fatigue and mental fatigue in patients with advanced cancer,8 while Havlikova et al. observed significant associations with general fatigue and reduced motivation in patients with Parkinson's disease.9 In the present study the characteristics of fatigue in the male patients are similar to those observed in the depressive state in the previous studies,7–9 although no significant change in reduced motivation. In contrast, the female patients in the present study had a higher tendency toward physical fatigue. Investigation into the reason for the variation exceeds the present study's reach, but it is suggested that sex hormone or social environment may be responsible for this. In the total or male subjects the existence of agoraphobia may not explain the significant difference in reduced activity between the patients and controls because no significant difference was observed in score between patients with and without agoraphobia (data not shown).

Several limitations may be considered for interpreting the results. One is the effect of subdiagnostic depressive state. To exclude the effect of depressive state, the present subjects did not include patients with coexisting mood disorders. In addition, the score for SDS-J was included as a covariate in comparison of the MFI-J scores. But correlation between the SDS-J and MFI-J scores was significant (Pearson correlations were 0.62, 0.70, 0.59, 0.61, and 0.62 for general fatigue, physical fatigue, mental fatigue, reduced motivation, and reduced activity, respectively, P < 0.001 for all analyses). In the patient comparison on the basis of severe cut-off score,6 there were significant differences in all MFI-J factors (Table 2). There was a significant difference in the score for SDS-J between the patients and controls (t = 9.84, P < 0.001, Student's t-test).Therefore it may be possible that the present results reflect subdiagnostic depressive state as well as panic disorder. To confirm the present results, further investigation is needed, such as comparing the MFI-J scores between panic disorder patients and depressive disorder patients. A second limitation involved the effect of medication. In the present study no correlation was observed between duration of illness or age of onset and the MIF-J or SDS-J scores after correction for multiple testing (data not shown), but dose of medication or therapeutic status was not controlled. A third limitation related to attributes of the controls, who consisted of volunteers from the general population. The history of mental disorder could not be completely excluded for privacy policy reasons.

Table 2.  MFI-J factors according to SDS-J score in panic disorder patients (mean ± SD)
 nSDS-JMFI-J factors
General fatiguePhysical fatigueMental fatigueReduced motivationReduced activity
  1. MFI-J scores were compared between patients with the SDS score <55 and >56 using Student's t-test.

  2. MFI-J, Japanese Version of the Multidimensional Fatigue Inventory; SDS-J, Self-rating Depression Scale – Japanese Version.

SDS-J < 5532539.0 ± 8.913.1 ± 3.512.0 ± 3.810.8 ± 3.79.5 ± 3.39.7 ± 3.7
SDS-J > 563560.9 ± 3.317.2 ± 2.318.0 ± 2.316.2 ± 2.814.3 ± 3.415.7 ± 3.2
t53.113.310.68.229.33
P<0.001<0.001<0.001<0.001<0.001

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