In all, 190 stroke patients were approached for participation. Seventy-five of those were excluded: 21 had recurrent stroke, 17 had cognitive impairment, 17 had aphasia, 10 were < 45 years, and 10 had a stroke duration > 2 years (Fig. 1). After applying the exclusion criteria, 115 stroke patients were enrolled. They comprised 63 males (54.8%) and 52 females (45.2%), with a mean age of 64 years (SD: 10 years; min, max: 45, 88). The majority had graduated primary school, followed by lower-secondary school and upper-secondary school. The comorbid illnesses found were, in descending order of frequency, hypertension, dyslipidemia, diabetes mellitus, and heart disease. The median duration of stroke was 59 days. The large majority of patients (81.7%) suffered from ischemic stroke, and left-side weakness was dominant (61%). Most patients (65.2%) were recruited from inpatient rehabilitation.
All patients were administered the PHQ-9 as the index test. The reference standard was the psychiatric interview conducted on the same day, with the resultant diagnosis based on the DSM-5 criteria. The psychiatrist who administered the interview was blinded to the corresponding score for the index test, and all interviews were conducted regardless of the index test scores. The mean Thai PHQ-9 score was 5.2 ± 4.8. According to the DSM-5 criteria, 23 patients (20%) were diagnosed with PSD, whereas 92 patients (80%) were normal. In the PSD group, eight (6.9%) were classified as having a major depressive disorder, two (1.7%) with an unspecified depressive disorder, and one (0.9%) with another specified depressive disorder. The remaining 12 patients (10.5%) were diagnosed as having an adjustment disorder with a depressed mood.
Table 1. The baseline characteristics of the stroke patients
Variables
|
Normal
(N=92)
|
PSD
(N=23)
|
P-value
|
Demographic-related
|
|
|
|
Age1
|
64.7 (9.5)
|
64.6 (12.2)
|
0.960
|
Gender2
|
54 (58.7)
38 (41.3)
|
9 (39.1)
14 (60.9)
|
0.092
|
Education level2
- Primary school
- Secondary school
- Bachelor degree and higher
|
42 (45.7)
26 (28.3)
24 (26.0)
|
13 (56.6)
5 (21.7)
5 (21.7)
|
0.430
|
Comorbid illness2
- Hypertension
- Dyslipidemia
- Diabetes mellitus
- Smoking
- Heart disease
|
77 (83.7)
53 (57.6)
37 (40.2)
21 (22.8)
19 (20.7)
|
21 (91.3)
17 (73.9)
12 (52.2)
4 (17.4)
6 (26.1)
|
0.518
0.152
0.300
0.572
0.572
|
Duration of stroke2
- <3 months
- 3-6 months
- >6 months
|
58 (63.0)
14 (15.2)
20 (21.7)
|
16 (69.6)
5 (21.7)
2 (8.7)
|
0.293
|
Pathology of stroke2
|
74 (80.4)
18 (19.6)
|
20 (87.0)
3 (13.0)
|
0.561
|
Side of weakness2
|
54 (58.7)
38 (41.3)
|
16 (69.6)
7 (30.4)
|
0.339
|
Setting2
|
60 (65.2)
32 (34.8)
|
15 (65.2)
8 (34.8)
|
0.793
|
Disability-related
|
|
|
|
Modified Rankin Scale2
|
7 (7.6)
16 (17.4)
18 (19.6)
50 (54.3)
1 (1.1)
|
2 (8.7)
0 (0.0)
3 (13.0)
15 (65.2)
3 (13.0)
|
0.036*
|
Depression-related
|
|
|
|
Median PHQ-9 score3
|
4.0
(0.5, 5.75)
|
10.0
(7.0, 15.0)
|
<0.001*
|
1 Mean (SD); 2 number (%); 3 median (IQR 25,75), *significant at p-value < 0.05
The demographic characteristics of the normal and depression groups revealed no statistically significant differences (Table 1). However, the MRS and the median PHQ-9 scores of the groups differed. MRS scores of 0–3 were defined as no-severe disability, while MRS scores > 3 were defined as severe disability; more stroke patients were disabled in the depression group (78%) than in the normal group (55.4%).
Reliability and item analysis
As presented in Table 2, the highest mean score of the nine PHQ-9 items was found for Item 3 (“trouble falling or staying asleep, or sleeping too much”). Item 9 (“thoughts that you would be better off dead or of hurting yourself”) had the lowest score. As to the internal consistency of the PHQ-9, Cronbach’s alpha was 0.78. All items, if deleted, would consistently decrease the total scale alpha. The least item-total correlation was for Item 5 (“poor appetite or overeating”).
Table 2. Mean score, standard deviation, and internal reliability score for each PHQ-9 score
PHQ-9 items
|
Mean
|
Standard deviation
|
Corrected item-total correlation
|
Cronbach's alpha if item deleted
|
1. Little interest or pleasure in doing things
|
0.72
|
0.881
|
0.612
|
0.708
|
2. Feeling down, depressed, or hopeless
|
0.64
|
0.926
|
0.516
|
0.723
|
3. Trouble falling or staying asleep, or sleeping too much
|
1.11
|
1.256
|
0.404
|
0.749
|
4. Feeling tired or having little energy
|
0.68
|
0.984
|
0.321
|
0.755
|
5. Poor appetite or overeating
|
0.47
|
0.955
|
0.199
|
0.773
|
6. Feeling bad about yourself – or that you are a failure
|
0.71
|
1.015
|
0.612
|
0.704
|
7. Trouble concentrating on things
|
0.27
|
0.641
|
0.345
|
0.749
|
8. Moving or speaking so slowly that other people have noticed
|
0.35
|
0.731
|
0.555
|
0.722
|
9. Thoughts that you would be better off dead or of hurting yourself
|
0.25
|
0.662
|
0.525
|
0.729
|
Validity analysis
A comparison was made of the performance of the Thai PHQ-9 against the diagnosis of depressive disorder (based on the DSM-5 criteria for depressive disorders as the standard). According to the DSM-5 criteria, 23 patients (20%) met the diagnosis of PSD. The median Thai PHQ-9 score for the depression group was 10 (IQR 25%, 75%: 7, 15) whereas the median score of the normal group was 4 (IQR 25%, 75%: 0.5, 5.75). The differences in the median PHQ-9 scores of the 2 groups were statistically significant.
Table 3. The performance of different PHQ-9 cut-off scores in detecting depression
Score
|
Sensitivity
(%) (95% CI)
|
Specificity
(%) (95% CI)
|
Positive predictive value
(%) (95% CI)
|
Negative predictive value
(%) (95% CI)
|
Positive likelihood ratio
(95% CI)
|
Negative likelihood ratio
(95% CI)
|
Accuracy
(95% CI)
|
Youden’s index
|
The algorithm-based diagnosis
|
≥ 10
|
34.8
(16.4, 57.3)
|
97.8
(92.4, 99.7)
|
80.0
(47.6, 94.6)
|
85.7
(81.6, 89.0)
|
16.0
(3.6, 70.3)
|
85.7
(81.6, 89.0)
|
85.2
(77.4, 91.2)
|
-----
|
The summed-item-based diagnosis
|
≥ 5
|
91.3
(71.9, 98.9)
|
65.2
( 54.6, 74.8)
|
39.6
(32.6, 47.2)
|
96.8
(88.8, 99.1)
|
2.62
(1.9, 3.6)
|
0.13
(0.04, 0.5)
|
70.4
(61.2, 78.6)
|
0.565
|
≥ 6
|
87.0
(66.4, 97.2)
|
75.0
(64.9, 83.4)
|
46.5
(37.1, 56.2)
|
95.8
(88.8, 98.5)
|
3.5
(2.4, 5.1)
|
0.2
(0.1, 0.5)
|
77.4
(68.6, 84.7)
|
0.620
|
≥ 7
|
78.3
(56.3, 92.5)
|
81.5
(72.1, 88.8)
|
51.4
(39.6, 63.1)
|
93.8
(87.3, 97.0)
|
4.2
(2.6, 6.8)
|
0.3
0.1, 0.6
|
80.9
(72.5, 87.6)
|
0.598
|
≥ 8
|
65.2
(42.7, 83.6)
|
83.7
(74.5, 90.6)
|
50.0
(36.6, 63.4)
|
90.6
(84.5, 94.4)
|
4.0
(2.3, 6.9)
|
0.42
(0.2, 0.7)
|
80.0
(71.5, 86.9)
|
0.489
|
≥ 9
|
56.5
(34.5, 76.8)
|
90.2
(82.2, 95.4)
|
59.1
(41.4, 74.7)
|
89.3
(83.8, 93.0)
|
5.8
(2.8, 11.8)
|
0.5
(0.3, 0.8)
|
83.5
(75.4, 89.7)
|
0.467
|
≥ 10
|
52.2
(30.59, 73.2)
|
94.6
(87.7, 98.2)
|
70.6
(48.4, 85.9)
|
88.8
(83.7, 92.4)
|
9.6
(3.7, 24.5)
|
0.5
(0.3, 0.8)
|
86.1
(78.4, 91.8)
|
0.467
|
When using the algorithm-based diagnosis, an assessment of the validity of the Thai PHQ-9 index test revealed a sensitivity of 34.8%, specificity of 97.8%, positive predictive value of 80%, negative predictive value of 85.7%, and positive likelihood ratio of 16.0 (Table 3). As to using the summed-scored-based diagnosis, the corresponding values for different PHQ-9 thresholds in diagnosing PSD are detailed in Table 2. The cut-off score of 6 showed the highest Youden’s index. This cut-off score had a sensitivity of 87.0 % (95% CI: 66.4, 97.2), specificity of 75.0% (95% CI: 64.9, 83.4), positive predictive value of 46.5% (95% CI: 37.1, 56.2), negative predictive value of 95.8% (95% CI: 88.8, 98.5), positive likelihood ratio of 3.5 (95% CI: 2.4, 5.1), and negative likelihood ratio of 0.2 (95% CI: 0.1, 0.5). The ROC curve illustrates that the PHQ-9 performed well in identifying patients with PSD (Figure 2). The AUC in our study was 0.87 (95% CI: 0.78, 0.96), which represents good discrimination.