Appendix
Table A1– Comparison of signs and symptoms in the Centers for Diseases Control-1994, Canadian and Epidemiological
Case Definition for diagnosing ME/CFS
CDC-1994 Canadian Epidemiological Case
Signs and/or symptoms presented
criteria
Clinical
Definition
Definition
Level 1
Level 2
Persistent or recurrent tiredness/fatigue that persists after rest,
√
√
√
and is not due to over exercising or over work.
Tiredness/fatigue present for 6 months or more
Activities (personal, social, professional, and home chores) have
been affected by the symptoms of tiredness/fatigue. Some
activities were reduced or the patient can no longer perform them.
Activities were reduced to less than 50% (half) than before the
onset
The tiredness/fatigue is debilitating and affects the mental and
physical functioning
Infection at onset (confirmed or not by laboratory)
There is no illness that explains the symptoms of
tiredness/fatigue
Symptoms persistently or often present during the last 6 months
or longer
1. Memory or concentration problems
2. Sore throat
3. Tender glands in the neck or arm pit
4. Pain in two or more joints without swelling or redness
5. Headaches which are different/worse than you might had
before
6 Unrefreshing sleep
7 Malaise after exertion/effort (lasting more than 24 hours)
8. Muscle pain
9. Muscle discomfort
10. Unexplained weakness in muscles around the body
11. Joint pains moving to different joints but no swelling nor
redness
12. Fatigue after exercise/ effort (for more than 24 hours)
13. Intolerance to exercise (it is difficult to exercise)
14 Mild fever or chills
15. Confusion or disorientation
16. Difficulty in understanding things
17, Difficulty thinking
18. Unusual sensitivity to light or noise
19. Migraine which is different/worse than you might had before
20. Sleep problems in quality or duration (other than sleep
apnoea)
21. Anxiety
22. Depression
23.Intolerance (difficulty) to be on your feet (upright)
24 Unusual sweatiness or cold hands and feet
√
√
√
√
√
√
√
√
√ or
√
√*
√
√
√*
√*
√*
√* or
√* or
√*
√*
√
√
√*
√*
√*
√
√
√*
√*
√*
√
√*
√*
√***
√**
√**
√**
√**
√*
√*
√*
√*
√
√*
√*
√*
√*
√*
√**
√***
√***
√*
√*
√*
√*
√ or
√*
√*
√*
√
√***
√***
√*
√*
CDC-1994: All marked with √, plus at least 4 of the marked with √*
Canadian Criteria: All marked with √(fatigue, post=exertion malaise and sleep dysfunction); and at least 1 marked with
√*(pain); and at least 2 marked with √**(neurocognitive manifestations); and at least 2 marked with
√***( Autonomic, neuroendocrine and immune manifestations)
ECD: level 1- All marked with √, plus at least 4 of the marked with √*; level 2: All conditions for level 1, plus all marked
with √, plus at least 5 of the marked with √*. Excludes anxiety + depression.
Table A2 – Proportion of reported symptoms according to study case definitions*
All cases CDC-1994
Current symptoms
(n = 170)
(n=166)
Sleep dysfunction Unrefreshing sleep
97.1
97.6
Sleep problems
86.4
87.3
Neurological
Memory/concentration problems
94.1
94.0
/Cognitive
Difficulty thinking
85.2
86.1
manifestations
Unexplained muscle weakness
79.7
79.9
Light/noise sensitivity
67.9
68.3
Difficulty in understanding things
63.6
64.6
Confusion or disorientation
55.7
56.4
Pain
Pain in two or more joints
88.8
89.2
Muscle pain
90.5
90.9
Muscle discomfort
87.0
87.9
Migratory joint pain
74.7
74.7
Canadian
(n=96)
ECD
(n=22)
100.0
95.4
94.8
68.2
99.0 100.0
94.8
76.2
89.6
72.7
82.1
59.1
78.5
60.0
77.7
52.4
93.7
86.4
96.9
81.8
93.7
77.3
83.3
59.1
Headaches
62.7
63.0
75.0
54.5
Migraine
29.2
29.3
37.8
22.7
Fatigue/tiredness
Fatigue after exercise (>24 h)
84.0
83.6
100.0
90.9
Intolerance to exercise
79.2
76.2
88.4
81.8
Malaise after exertion (>24h)
78.4
79.1
91.6
86.4
Psychological
Anxiety
74.0
75.8
84.4
31.8
Depression
61.7
62.7
72.2
5.3
Autonomic
Sweatiness/ cold hands and feet
67.1
68.7
89.6
38.1
Intolerance to be on your feet
65.1
65.4
80.8
63.6
Immunological
Sore throat
54.2
54.9
70.5
45.4
Tender glands in the neck/armpits
57.4
58.2
75.0
45.4
Mild fever or chills
55.1
55.8
76.8
31.8
*All cases complying with each of the definitions are shown in the columns; therefore cases meeting more than
one diagnostic criterion appear more than once.