Table 1 Characteristics of patients according to post-exertional malaise severity quartiles

Epidemiological data

 Patients, n (%)

23 (11.7)

74 (37.6)

73 (37.1)

27 (13.7)

 Females, n (%)

17 (73.9)

58 (78.4)

50 (68.5)

21 (77.8)

 Basal metabolic index, kg/m²

23.7 [20.2–26.3]

23.3 [20.3–25.9]

22.5 [19.6–25.9]

21.9 [20.1–24.6]

 Age at disease onset, years

28 [21–38]

32 [25–41]

32 [27–39]

38 [31–41]

 Delay in diagnosis, months

60 [25–108]

62 [29.6–120]

44 [21–95]

26 [17–54]

Fatigue features

 Fatigue severity scale

5.4 [5–6] (n = 18)

5.5 [5.03–6.2] (n = 58)

5.9 [5.15–6.5] (n = 59)

5.9 [5.2–6.7] (n = 17)

 Fatigue scale

24 [18–27.5] (n = 15)

21 [18–25.5] (n = 59)

25 [22–28] (n = 61)

26 [22–28] (n = 21)

 MFIS^b physical

29.5 [26.5–32] (n = 16)

28 [24.3–31.8] (n = 58)

31 [27–33] (n = 59)

30 [26.5–33] (n = 22)

 MFIS cognitive

24 [19–34] (n = 16)

26 [19.2–30] (n = 58)

31 [24.5–33.5] (n = 59)

26 [22.3–30.6] (n = 22)

 MFIS psychosocial

6 [5–7] (n = 16)

5 [4–6] (n = 58)

6 [5–8] (n = 59)

6 [5–7] (n = 22)

Symptom clusters^c, n (%)

Neurological impairments

23 (100)

74 (100)

73 (100)

27 (100)

 Neurocognitive impairments

23 (100)

74 (100)

73 (100)

27(100)

  Difficulty processing information

23 (100)

68 (91.9)

70 (95.9)

27 (100)

  Short-term memory loss

16 (69.6)

62 (83.8)

66 (90.4)

24 (88.9)

 Pain

22 (95.7)

72 (97.3)

71 (97.3)

26 (96.3)

  Headaches

16 (69.6)

53 (71.6)

56 (76.7)

21 (77.8)

  Significant pain

19 (82.6)

64 (86.5)

68 (93.2)

26 (96.3)

 Sleep disturbances

22 (95.7)

74 (100)

72 (98.6)

27 (100)

  Disturbed sleep patterns

21 (91.3)

65 (87.8)

64 (87.7)

22 (81.5)

  Unrefreshed sleep

21 (91.3)

74 (100)

69 (94.5)

25 (92.6)

 Neurosensory, perceptual and motor disturbances

22 (95.7)

73 (100)

73 (100)

27 (100)

  Neurosensory and perceptual troubles

20 (87)

62 (83.8)

69 (94.5)

23 (85.2)

  Motor disturbances

20 (87)

69 (93.2)

69 (94.5)

27 (100)

 Immune, gastrointestinal, and genitourinary impairments

21 (91.3)

66 (89.2)

71 (97.3)

24 (88.9)

  Flu-like symptoms

16 (69.6)

50 (67.6)

59 (80.8)

19 (70.4)

  Susceptibility to viral infections

3 (13)

26 (35.1)

31 (42.5)

12 (44.4)

  Gastrointestinal impairments

17 (73.9)

63 (85.1)

60 (82.2)

22 (81.5)

  Genitourinary impairments

2 (8.7)

28 (37.8)

29 (39.7)

7 (25.9)

  Sensitivities to food, medications, odors, or chemicals

2 (8.7)

6 (8.1)

4 (5.5)

35 (11.1)

 Energy production/transportation impairments

22 (95.7)

74 (100)

72 (98.6)

27 (100)

  Cardiovascular manifestations

19 (82.6)

72 (97.3)

65 (89)

27 (100)

  Respiratory manifestations

9 (39.1)

36 (48.6)

38 (52.1)

19 (70.4)

  Loss of thermostatic instability

18 (78.3)

65 (87.8)

61 (83.6)

26 (96.3)

  Intolerance of extremes of temperatures

13 (56.5)

61 (82.4)

42 (57.5)

21 (77.8)