Table 2.
Comparison of patients according to blood lactate levels at rest.
| Elevated lactate | Normal lactate | p | |
|---|---|---|---|
| Epidemiological characteristics | |||
| Patients, n (%) | 55 (44.7) | 68 (55.3) | |
| Female/Male | 35/20 | 54/14 | 0.052 |
| Duration of illness (months) | 60 [63–96] | 78 [36–144] | 0.11 |
| Age at disease onset (years) | 36 [25.5–42] | 32 (26–39] | 0.26 |
| Fatigue features | |||
| Fatigue severity scale |
(n = 43) 5.6 [4.8–6.2] |
(n = 53) 5.4 [5.1–6] |
0.90 |
| Fatigue scale |
(n = 46) 24 [21–28] |
(n = 57) 23 [17–27] |
0.14 |
|
Modified fatigue impact scale Physical subscale Cognitive subscale Psychosocial subscale |
(n = 47) 28 [24–32] 28 [20–33] 6 [4–7] |
(n = 57) 30 [27–32] 26 [20–32] 6 [4–6] |
0.09 0.59 0.43 |
| Patients’ comorbidities, n (%) | |||
| Reactive depression | 15 (27.3) | 21 (30.9) | 0.66 |
| Fibromyalgia | 8 (14.6) | 11 (16.2) | 0.80 |
| Irritable bowel syndrome | 18 (32.7) | 32 (47.1) | 0.11 |
| Clinical manifestations n (%) | |||
| More severe post-exertional malaise* | 34 (61.8) | 28 (41.2) | 0.02 |
| Difficulty processing information | 54 (98.2) | 64 (94.1) | 0.26 |
| Short-term memory loss | 46 (83.6) | 55 (80.9) | 0.69 |
| Headaches | 42 (76.4) | 47 (69.1) | 0.37 |
| Myalgia | 50 (90.9) | 57 (83.8) | 0.25 |
| Arthralgia | 36 (65.5) | 36 (53) | 0.16 |
| Disturbed sleep patterns | 51 (92.7) | 58 (85.3) | 0.20 |
| Unrefreshed sleep | 51 (92.7) | 67 (98.5) | 0.11 |
| Neurosensory and perceptual disturbances | 48 (87.3) | 66 (97.1) | 0.16 |
| Motor disturbances | 50 (90.9) | 61 (89.7) | 0.56 |
| Flu-like symptoms | 42 (76.4) | 50 (73.5) | 0.72 |
| Recurrent infections | 25 (45.5) | 22 (32.4) | 0.14 |
| Gastrointestinal impairments | 43 (78.2) | 62 (91.2) | 0.63 |
| Urinary impairments | 15 (27.3) | 23 (33.8) | 0.43 |
| Orthostatic intolerance | 15 (27.3) | 26 (38.2) | 0.20 |
| Palpitation | 35 (61.8) | 44 (64.7) | 0.90 |
| Laboratory abnormalities, n (%) | |||
| Serum zinc deficit† | 20 (36.4) | 19 (28) | 0.31 |
| Serum 25-hydroxyvitamin D deficit‡ | 31 (56.4) | 30 (44.1) | 0.18 |
| Low plasma 8 am and/or 8 pm cortisol levels§ | 10 (18.2) | 13 (19.1) | 0.90 |
Notes: *Score ≥12 on Centres for Disease Control and Prevention Symptom Inventory auto-questionnaire. †Normal range = 0.70–1.25 mg/L, measured by atomic emission spectroscopy/high-frequency induction plasma. ‡Normal range = 75–250 nmol/L, measured by chemiluminescence technology (CLIA). §Normal values = 5–49 µg/L at 8 am, and 30–100 µg/L at 8 pm, measured by Immunoenzymatic chemoluminescznce (12000 ABBOT) method. Cortisol deficit was retained if one or both measurements were reduced. Categorical data were expressed as absolute number and percentage. Continuous data were expressed as median and interquartiles.