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Diagnostics 2019, 9(1), 26; https://doi.org/10.3390/diagnostics9010026

Article
Assessment of Post-Exertional Malaise (PEM) in Patients with Myalgic Encephalomyelitis (ME) and Chronic Fatigue Syndrome (CFS): A Patient-Driven Survey
Center for Community Research, Department of Psychology, DePaul University, Chicago, IL 60604, USA
*
Author to whom correspondence should be addressed.
Received: 1 February 2019 / Accepted: 26 February 2019 / Published: 2 March 2019

Abstract

:
Considerable controversy has existed with efforts to assess post-exertional malaise (PEM), which is one of the defining features of myalgic encephalomyelitis (ME) and chronic fatigue syndrome (CFS). While a number of self-report questionnaires have been developed to assess this symptom, none have been comprehensive, and a recent federal government report has recommended the development of a new PEM measure. The current study involved a community-based participatory research process in an effort to develop a comprehensive PEM instrument, with critical patient input shaping the item selection and overall design of the tool. A survey was ultimately developed and was subsequently completed by 1534 members of the patient community. The findings of this survey suggest that there are key domains of this symptom, including triggers, symptom onset, and duration, which have often not been comprehensively assessed in a previous PEM instrument. This study indicates that there are unique benefits that can be derived from patients collaborating with researchers in the measurement of key symptoms defining ME and CFS.
Keywords:
myalgic encephalomyelitis; chronic fatigue syndrome; post-exertional malaise; assessment; patient-driven questionnaire; participatory research

1. Introduction

Among patients with myalgic encephalomyelitis (ME) and chronic fatigue syndrome (CFS), post-exertional malaise (PEM) has long been considered a hallmark symptom [1]. However, in a field which includes more than twenty case definitions for ME and CFS, there has not been agreement regarding defining PEM [2]. For example, discrepancies occur with two of the most frequently used ME and CFS case definitions, the Fukuda [3] and Canadian Consensus Criteria (CCC; [4]). The Fukuda et al. criteria do not define the term beyond requiring that it last for more than 24 h nor does it make PEM a requirement for diagnosis. In contrast, the CCC case definition requires the presence of PEM for diagnosis and goes further to describe the symptomatic experience as similar to flu-like distress, with a potential delayed onset [4].
Several activity and self-report measurements that assess the extent of activity and how such activity might result in exacerbation of symptoms have been proposed to measure PEM. These include actigraphy, exercise challenges, time logs, and self-reports [5]. For example, following an exercise task, Mateo et al. [6] reported a broad spectrum of PEM-related symptoms including fatigue, muscle/joint pain, cognitive dysfunction, decrease in function, headaches, sleep disturbances, pain, weakness, cardiopulmonary symptoms, lightheadedness, and flu-like symptoms. Others have found using self-report measures that PEM comprises two distinct constructs: muscle-specific fatigue and generalized fatigue [7].
Factors which elicit PEM include physical and cognitive exertion. For some patients, even basic activities of daily living such as toileting, bathing, dressing, communicating, and reading can trigger PEM. However, many patients feel that potential triggers should extend beyond these types of stressors and include infections [8], exposure to chemicals or certain foods [9], or exposure to certain metals [10]. Additionally, many efforts to assess PEM have not included a characteristic delay in the onset of PEM. Chu et al. [11] maintain that this delay is rarely found in other fatiguing illnesses. Another issue that has often not been included in the assessment of PEM is that many patients with ME and CFS take considerably longer to recover from a trigger [12], reporting a substantial increase in symptoms immediately after an exercise test, the next day, and even a week later [13].
In an effort to address these PEM-related discrepancies, the National Institutes of Health/Center for Disease Control and Prevention (NIH/CDC) Common Data Element (CDE) committee’s PEM working group attempted to define PEM [14] as “an abnormal response to minimal amounts of physical or cognitive exertion that is characterized by: (1) Exacerbation of some or all of an individual study participant’s ME/CFS symptoms. (2) Loss of stamina and/or functional capacity. (3) An onset that can be immediate or delayed after the exertional stimulus by hours, days, or even longer. (4) A prolonged, unpredictable recovery period that may last days, weeks, or even months. (5) Severity and duration of symptoms that is often out-of-proportion to the type, intensity, frequency, and/or duration of the exertion.” Yet, there was no set of items with anchor points associated with these 5 descriptors of PEM offered by the NIH/CDC CDE PEM working group. While the general guidance of the committee was helpful, these types of general descriptions need to be operationalized if investigators are to reliably use them to assess PEM. The NIH/CDC CDE’s PEM working group also recommended the use of 5 items from the DePaul Symptom Questionnaire (DSQ, [12]) to measure PEM (e.g., physically drained or sick after mild activity). However, the DSQ was not developed as a comprehensive measure of PEM but rather as a measure of ME and CFS symptomatology as a whole. Following the release of the NIH/CDC CDE’s PEM recommendations, patients were extremely concerned with the recommendations that had been made [15].
This latest NIH/CDC CDE’s recommendations regarding the measurement of PEM needs to be understood in the context of a long history where patients have felt left out of key policy decisions imposed on them, including how to name, define, and treat ME and CFS. As one example, when the Institute of Medicine (IOM; [16]) recommended a new name and case definition, this created considerable controversy, as many feel that both were decisions imposed on the patient community, without first seeking their input and approval.
The recent recommendations made by this NIH/CDC CDE’s PEM working group, and the vociferous reactions to it by the patient community, provided an opportunity to engage in community-based participatory research, which equitably involves all partners in the research process [17]. Given the importance of PEM, and the patient community’s resentment regarding once again not being active participants in the development of this latest PEM recommendation, the current authors decided to try to develop a comprehensive measure with active collaboration of the patient community. We hypothesized that a valid PEM instrument could be created with the help of the patient community.

2. Materials and Methods

2.1. Methods and Participants

The study began with dialogue between Leonard Jason and a number of leading patient activists who were unhappy with the NIH/CDC CDE’s PEM recommendations. A patient poll had indicated that the patient community preferred the NIH/CDC general description of PEM rather than the 5 DSQ items [15], but those general PEM descriptors had not been operationalized in any systematic way. Jason and several patient activists reworked those descriptors into a usable questionnaire, and this was posted on Facebook, Twitter, and LinkedIn social media pages and were widely shared with patient groups internationally. Hundreds of emails were received during the next three months, and Jason and Holtzman posted nine revisions of the survey for patients to provide comments. The comments and items received helped shape each new revision of the questionnaire. For example, when one participant commented “I also experience different types of PEM. I have the immediate PEM, where I do too much… But if I stop [exerting myself], these [PEM symptoms] go away fairly quickly… But if I am not able to stop during this immediate PEM stage and have to push on while experiencing these symptoms, then I get the “Post-PEM” usually two or more days later,” we used this input to introduce survey items that asked about both the immediate and delayed onset of PEM and its relationship to potential triggers.
After several months, when we were receiving few additional patient comments regarding our survey that we had been posting, we decided to collect data using this survey with the next phase of this project. Institutional Review Board (IRB) approval was obtained for collecting data based on the survey that had been developed using input from the patient community. Participants provided informed consent. Participants were required to be over the age of 18 years old, able to read and write in English, and have a current self-reported diagnosis of ME and/or CFS. Participants completed the questionnaire online using Research Electronic Data Capture (REDCap), a secure online survey tool [18]. Respondents were instructed to save their answers and return to complete the survey at a later time if they were not able to finish the survey in one sitting due to their illness.

2.2. Materials

The first part of the survey assessed demographic characteristics, as well as information about illness/diagnosis status (see Table 1). Following this background assessment, the respondents were asked about the onset of their PEM symptoms (see Table 2), and then asked questions relating to factors that trigger PEM (Table 3). This included examples of triggers beyond physical or cognitive exertion, such as “basic activities of daily living”, “positional changes”, and “emotional events”. The survey also asked specific questions about the relationship between triggers of PEM and other factors, such as participants’ individual energy limits or the extent to which they may exert themselves.
Next, the participants were asked to evaluate a list of symptoms that are exacerbated following physical and/or cognitive exertion (Table 4). The symptoms included items which have been assessed through other operationalized measures (e.g., “physical fatigue”, “unrefreshing sleep”, and “flu-like symptoms”), as well as items suggested by patients (e.g., “physical fatigue while mentally wired”, “brain twangs” and “burning sensation all over your skin”). Each item was rated for frequency for the past six months on a 5-point Likert scale: 0 = none of the time, 1 = a little of the time, 2 = about half the time, 3 = most of the time, 4 = all of the time. Symptoms of 2 or higher were considered to be the threshold for PEM, based on past studies [19]. For each symptom, frequency values were multiplied by 25 to convert to 100-point scales, with higher values indicating more frequent symptoms.
Table 5 shows item responses of participant experiences of PEM by asking the question “If you go beyond your energy limits by engaging in pre-illness tolerated exercise or activities of daily living, do you experience any of the following?” Several common phrases used to describe PEM were then listed, including “a severity and duration of symptoms that are out of proportion to the initial trigger” and “global worsening of multi-systemic symptoms (an example of this might be aches all over your body plus cognitive problems plus light and/or sound sensitivity)”.
Following the PEM symptom list, the survey included an assessment of duration of PEM and length of recovery time, as well as information about illness course and functioning (Table 6). To better understand the relationship between PEM and exertion, participants were asked if the severity and duration of PEM was out-of-proportion to the type, intensity, frequency, and duration of exertion. Participants were then asked whether they had ever experienced an “adrenaline surge” after going beyond their energy limit, and how long the surge lasts before the onset of PEM. Next, patients were assessed on their illness course and functional status by asking how long ago they began feeling sick with ME or CFS, if the illness has been present for at least 50% of the time, and how they would describe their illness and functioning. Participants were also asked if they are managing their PEM symptoms by pacing or “staying within their energy envelope,” one of the few patient recommended treatments for ME and CFS [20].
The survey also requested information about past tests the participant may have completed, such as a cardiopulmonary or tilt table test. Lastly, the survey assessed if the participants felt that this patient-driven survey accurately depicts their PEM experience.

3. Results

The international online convenience sample included 1,534 adults identifying as having ME and/or CFS who completed the questionnaire (347 additional respondents had incomplete surveys and were not included in this analysis). Respondents were from over 35 countries. As indicated in Table 1, 41.1% of participants reported currently living in the United States. The sample consisted of mostly females (84.6%). The majority of participants were white/Caucasian (97.5%), and 2% identified as being of Latino or Hispanic origin. Just over half of the participants were married or living with a partner (56.6%), 39.3% had a standard college degree, and 45.7% were receiving disability payments.
Table 1 indicates that 50.7% of participants had a diagnosis of CFS, 22.0% had a diagnosis of ME, and 27.2% had a diagnosis of both ME and CFS. For our entire sample, 94.4% reported being diagnosed by a medical doctor.
Descriptive statistics of PEM onset are reported in Table 2. Over half of participants had experienced onset of symptom exacerbation immediately after exertion (72.3%), while 91.4% had experienced delayed onset after exertion. To determine the length of the delay between exertion and the onset of PEM, participants selected periods for when the onset of PEM might occur when onset is delayed. A delay of between 1–2 days after exertion was experienced by 53.1% of the participants.
Table 3 describes PEM triggers, with 78.2% endorsing “basic activities of daily living”, 64.5% endorsing “positional changes”, and 93.2% endorsing “emotional stress (good or bad)”. Additionally, 84.9% said there were some instances in which the specific precipitants could not be identified. The highest endorsed non-exertion triggers reported by participants were as follows: emotional events (88.3%), noise (85.5%), and sensory overload (83.6%).
Table 4 reports the proportion of participants who endorsed the worsening of symptoms due to physical or cognitive exertion. The most commonly endorsed symptoms were as follows: reduced stamina and/or functional capacity (99.4%), physical fatigue (98.9%), cognitive exhaustion (97.4%), problems thinking (97.4%), unrefreshing sleep (95.0%), muscle pain (87.9%), insomnia (87.3%), muscle weakness/instability (87.3%), temperature dysregulation (86.9%), and flu-like symptoms (86.6%). The symptoms endorsed by less than half of the sample included the following: loss of appetite (49.0%), migraines (46.2%), cardiac pain and/or arrhythmia (41.2%), brain twangs (29.9%), burning sensation all over your skin (29.7%), paralysis/inability to move (29.4%), pre-menstrual symptoms (21.1%), and decreased heart rate (15.1%).
In order to gauge participant’s general experiences of PEM, participants were asked if they experienced any of the common phrases used to describe PEM (listed in Table 5) after exertion. All of the phrases were endorsed by over 90% of the sample.
The findings reported in Table 6 indicate that over half the participants (58.0%) said PEM lasts on average 3–6 days, with 1–2 days (38.9%), 1 week–1 month (46.7%), and 1–6 months (30.3%) also being frequently reported. Additionally, 67.1% of the sample had experienced a “crash” that never resolved. Over half of the sample (57.2%) said they had experienced an adrenaline surge during or after going beyond their energy limits, and the most commonly reported length of time was “a few hours” (35.8%). Further information about the natural history of participants’ ME/CFS illness are also provided in Table 6. The majority of subjects have been sick for over 10 years, with 97.1% reporting their illness being present for more than 50% of the time. Additionally, nearly half of participants described the course of their illness as fluctuating, experiencing good periods and bad periods. Lastly, nearly half of participants classified their status as being able to do light house work, but not being able to work part-time.
Table 6 also contains information on how participants were currently managing their PEM symptoms. Only 6% of patients with ME or CFS felt that pacing completely allowed them to avoid PEM, while the majority reported pacing only being effective some of the time and only at a moderate/mild level. Participants also identified the pacing method they used (e.g., 87.1% indicated it was based on their bodies’ reactions whereas 10.7% indicated it was with a heart rate monitor, and 17.3% indicated both).
Patients were also asked about tests to assess their cardiovascular health difficulties and orthostatic intolerance, which are common symptoms of ME and CFS and are often made worse after exertion. Almost a quarter (24.5%) indicated they had undergone a cardiopulmonary test and 29.7% indicated they had taken part in a stand lean/tilt table test. Of those patients, 9.3% had normal cardiopulmonary results, whereas 14.9% had abnormal results. Only 4.8% of the sample had completed an exercise test on back-to-back days.
At the end of the questionnaire, participants were asked if they felt this survey accurately captured their experiences of PEM, and 29.8% felt the survey was very accurate, 57.7% reported it was accurate, 10.7% were neutral, 1.2% thought it was not accurate, and 0.1% said it was not at all accurate.

4. Discussion

The objective of this study was to use community-based participatory research in an effort to develop a comprehensive way to assess PEM. Based on the comments and items suggested from patients, the following specific aspects of PEM were found to be the most critical domains: the timing of PEM onset, triggers of PEM, symptoms that are exacerbated following exertion or exposure to triggers, phrases used to describe consequences of PEM, duration of PEM, relationship between exertion and length of recovery, and the importance of considering personal characteristics (e.g., how long the patient has had ME/CFS, the course of their illness, their level of functioning, and coping methods used). The patient perspective provided the authors with the critical information to develop this survey of PEM. Of the patients who took part, 87.5% felt that the resulting survey was either very accurate or accurate.
Onset of symptom exacerbation after exertion was found to vary between patients. As shown in Table 2, the majority of patients experienced both immediate and delayed onset of PEM, and the extent of the delay of symptoms varied considerably. In addition to the unpredictability of PEM onset, several factors affect the duration of PEM before recovery, including the type, intensity, frequency, and duration of the exertion (see Table 6). These findings are consistent with patients’ reporting of prolonged recovery from PEM symptoms. In one study in which patients and healthy controls participated in a fatiguing exercise test, the patient group’s recovery was prolonged [21]. In addition, VanNess et al. [13] found patients with CFS, in comparison to healthy controls, take considerably longer to recover after completing a maximal cardiopulmonary exercise test the next day and a week later. Our findings are also consistent with a study by Chu et al. [11] who found that when comparing PEM symptom onset between those with ME or CFS to healthy controls, 87‒95% of controls had recovered within 24 h after completing an exercise test. Among those with ME and CFS, PEM symptoms peaked at 24 to 48 h later, and 45‒60% still experienced symptoms up to 5 days later.
Our survey also assessed specific triggers that bring on symptom exacerbation. The effects of physical and cognitive exertion on PEM have been well-established [13,21,22,23] and these findings are consistent with the current study. For example, only 37% of subjects reported being able to exercise “a little” without PEM-related symptoms, as long as they stay within “certain limits” (see Table 3). Furthermore, basic activities of daily living (e.g., getting dressed, cooking a meal, bathing), positional changes (e.g., going from lying down to standing up), and emotional stress lead to exacerbation in 78.2%, 64.5%, and 93.2% of patients, respectively.
Another issue explored involved whether there are precipitants of PEM beyond physical or cognitive exertion. The highest reported triggers in addition to physical/cognitive exertion were emotional events (88.3%), noise (85.3%), and sensory (83.6%) and visual overload (79.7%). This is consistent with past literature reporting these types of stimuli as exacerbating symptoms [24]. It has also been hypothesized that exposure to mold could trigger illness onset and PEM symptomology [25]. In our sample, 39.4% reported mold triggering their PEM. This is consistent with findings by Brewer, Thrasher, Straus, Madison, and Hooper [26], where 30% of patients with ME and CFS were reported to have multiple mycotoxins present in their bodies.
Partly as a function of this survey and the interactions with the patient community, there have been several additional developments in the assessment of PEM. First, Cotler et al. [27] found that use of the 5 recommended PEM DSQ items was an excellent screen in identifying PEM in patients with ME and CFS. In addition, as a second step in the process of assessing PEM, 5 additional DSQ items (including the assessment of duration of symptoms) were successfully used to differentiate PEM from other chronic illnesses. In addition, the findings from the patient survey reported on in this article were revised in order to construct a briefer, more concise measure of PEM, which was significantly related to physical functioning [28].
There are several limitations to this study. First, we did not obtain confirmation of ME or CFS diagnoses by independent medical personnel. In addition, we do not know what case definitions, if any, were used in their diagnoses. In addition, consistent with other ME and CFS studies, the sample was not demographically diverse. However, having a sample from several geographic regions did increase the generalizability of findings. Another limitation of the study was the length of the questionnaire. Though participants were presented with the option of pausing, it is reasonable that some may have still found it difficult to complete.
The open, participatory nature of this study provided a unique way of both designing the survey and gathering comprehensive information from the ME and CFS community regarding PEM. There are unique benefits that can accrue to the research and patient community by actively collaborating on instrument development as well as other policy issues, such as the selection of a name for the illness as well as the case definition [29]. By collaborating with the ME and CFS community, we have provided a model of community-based participatory research, which has multiple advantages to both the patient and research communities [30]. We close with this quote regarding what needs to occur to further this type of collaborative research in the ME and CFS areas:
“An alternative vision is still possible if those in power are willing to bring all interested parties to the table, including international representatives, historians on the science of illness criteria, and social scientists adept at developing consensus. In a collaborative, open, interactive, and inclusive process, issues may be explored, committees may be charged with making recommendations, and key gatekeepers may work collaboratively and transparently to build a consensus for change. Involve all parties—patients, scientists, clinicians, and government officials—in the decision-making process [31].”

Author Contributions

Investigation, formal analysis, and writing—original draft, C.S.H.; writing—review and editing, S.B. and J.C.; conceptualization, supervision, and writing—review and editing, L.A.J.

Funding

This research received no external funding.

Acknowledgments

The authors thank the ME and CFS patient community for their collaborative efforts.

Conflicts of Interest

The authors declare no conflicts of interest.

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Table 1. Demographic characteristics of patients with myalgic encephalomyelitis (ME) and chronic fatigue syndrome (CFS) (N = 1534).
Table 1. Demographic characteristics of patients with myalgic encephalomyelitis (ME) and chronic fatigue syndrome (CFS) (N = 1534).
AgeM (SD)
51.26 (13.08)
Gender% (n)
Female84.6 (1,298)
Male14.9 (229)
Race% (n)
White/Caucasian97.5 (1,495)
Black/African American0.3 (4)
American Indian or Alaska Native0.7 (11)
Asian or Pacific Islander1.1 (17)
Latino/Hispanic Origin2.0 (30)
Prefer not to respond1.4 (22)
Marital Status% (n)
Married or living with partner56.6 (869)
Never married23.3 (357)
Divorced13.9 (213)
Separated2.6 (40)
Widowed2.0 (31)
Prefer not to answer1.2 (19)
Education Level% (n)
Graduate/professional degree29.1 (446)
Standard college/university degree39.3 (603)
Partial college22.1 (339)
High school or General Education Development (GED)5.9 (91)
Some high school2.5 (39)
Less than high school0.8 (12)
Employment Status% (n)
On disability45.7 (701)
Working full-time6.8 (104)
Working part-time13.2 (203)
Homemaker7.3 (112)
Student3.3 (50)
Retired18.1 (278)
Unemployed16.0 (245)
Prior to leaving the workforce, did you cut back either in number of hours worked or in responsibilities57.5 (880)
Diagnosis% (n)
CFS50.7 (777)
ME22.0 (338)
Both ME and CFS27.2 (418)
Who diagnosed you?% (n)
Medical doctor94.4 (1448)
Was the medical doctor an expert/knowledgeable of ME/CFS?55.6 (853)
Alternative practitioner5.5 (85)
Self-diagnosed7.6 (117)
Current Annual Income (in US dollars)% (n)
Less than $24,99952.2 (801)
$25,000 to $49,99914.7 (225)
$50,000 to $99,9998.3 (128)
$100,000 to $149,9992.8 (43)
$150,000 to $199,9990.9 (14)
$200,000 to $249,9990.2 (3)
$250,000 or more1.0 (16)
Prefer Not to Respond18.1 (277)
Annual Income prior to becoming ill (in US dollars)% (n)
Less than $24,99915.4 (237)
$25,000 to $49,99925.0 (384)
$50,000 to $99,99925.4 (390)
$100,000 to $149,9996.7 (103)
$150,000 to $199,9991.8 (27)
$200,000 to $249,9991.2 (18)
$250,000 or more1.7 (26)
Prefer Not to Respond19.9 (305)
Note: Percentages may not add up to 100% due to missing data. For employment status, there were also several open response questions asking about what conditions participants received disability for, and for current and past job titles.
Table 2. Onset (N = 1534).
Table 2. Onset (N = 1534).
Items% (n)
Immediate onset of symptom exacerbation72.3 (1109)
All the time9.9 (152)
Most of the time21.9 (336)
About half the time24.1 (369)
A little of the time15.6 (239)
Delayed onset of symptom exacerbation91.4 (1402)
All the time21.8 (335)
Most of the time37.1 (569)
About half the time23.4 (359)
A little of the time8.1 (125)
How long after the exertion does your symptom exacerbation occur *
1 h or less16.5 (253)
2–6 h33.1 (508)
7–12 h31.0 (476)
13–24 h43.2 (662)
1–2 days53.1 (815)
3–4 days15.7 (241)
5–6 days4.5 (69)
More than 1 week4.2 (65)
Note: * For this item, participants could select more than one answer. There is also an option for participants to describe what activities and which symptoms affect immediate and/or delayed onset.
Table 3. Triggers (N = 1534).
Table 3. Triggers (N = 1534).
Items% (n)
Basic activities of daily living trigger symptom exacerbation78.2 (1199)
All of the time20.8 (319)
Most of the time24.1 (370)
About half the time17.7 (272)
A little of the time15.3 (234)
Positional changes lead to symptom exacerbation64.5 (990)
All of the time14.9 (229)
Most of the time20.0 (307)
About half the time15.5 (238)
A little of the time13.9 (213)
Emotional stress (good or bad) lead to symptom exacerbation93.2 (1429)
All of the time34.0 (522)
Most of the time29.2 (448)
About half the time18.3 (280)
A little of the time11.5 (177)
Instances in which the specific precipitants cannot be identified84.9 (1302)
Able to exercise a little as long as you stay within certain limits without symptom exacerbation37.0 (567)
Takes less exposure than usual to trigger PEM on days you are recovering from symptom exacerbation94.3 (1447)
Sensitized to particular triggers so they cause an even more abnormal response over time48.1 (738)
Severity of the PEM reaction proportionate to how far beyond your limits you have gone80.9 (1241)
Mild overexertion over several days produces an abnormal physical or cognitive response96.8 (1485)
Multiple occurrences of PEM that cause your overall health status to become worse over weeks/months84.4 (1295)
Intolerance to stimulation causes worsening in symptoms, but is not prolonged if stimulus is removed79.5 (1219)
Fighting off an infection (flu, cold, bladder infection) causes a worsening in all/most of your symptoms82.3 (1262)
Length of time for recovery correlates with the severity of PEM79.6 (1221)
Do you have other triggers such as
Emotional events (good or bad)88.3 (1354)
Noise85.3 (1308)
Sensory overload83.6 (1282)
Visual overload79.7 (1223)
Heat74.4 (1141)
Light68.8 (1055)
Cold66.3 (1017)
Foods61.0 (935)
Chemicals58.0 (889)
Watching movement (such as watching a video)52.5 (806)
Vibration47.1 (722)
Drugs used for medication47.4 (727)
Mold39.4 (605)
Supplements27.4 (420)
Table 4. Symptoms made worse due to physical or cognitive exertion (N = 1534).
Table 4. Symptoms made worse due to physical or cognitive exertion (N = 1534).
Items% (n) “Yes”% (n) at “2” ThresholdMean (SD)
1. Reduced stamina and/or functional capacity99.4 (1525)98.0 (1504)90.60 (17.16)
2. Physical fatigue98.9 (1517)98.3 (1508)87.53 (18.26)
3. Cognitive exhaustion97.4 (1494)92.0 (1412)77.64 (24.87)
4. Problems thinking97.4 (1494)92.6 (1420)78.47 (24.87)
5. Unrefreshing sleep95.0 (1457)91.1 (1398)80.57 (27.65)
6. Muscle pain87.9 (1349)81.5 (1250)69.41 (33.95)
7. Insomnia87.3 (1339)75.1 (1152)62.40 (34.30)
8. Muscle weakness/instability87.3 (1339)77.2 (1185)64.03 (33.86)
9. Temperature dysregulation86.9 (1333)75.2 (1153)63.76 (34.75)
10. Flu-like symptoms86.6 (1329)74.4 (1142)59.52 (33.43)
11. Aches all over your body85.6 (1313)79.5 (1219)68.68 (35.58)
12. Physically fatigued while mentally wired82.1 (1259)72.8 (1116)59.00 (35.65)
13. Dizziness80.7 (1238)56.0 (859)46.28 (33.19)
14. Gastro-intestinal problems78.6 (1206)59.3 (910)49.90 (36.02)
15. Headaches78.0 (1197)56.5 (866)46.48 (34.52)
16. Ataxia77.6 (1191)57.8 (886)47.62 (35.18)
17. Increased heart rate/heart palpitations  77.4 (118)64.9 (996)52.28 (36.51)
18. Weak or stiff neck74.6 (1144)61.0 (936)51.35 (38.20)
19. Joint pain73.0 (1120)59.5 (912)49.17 (37.86)
20. Problems with speech72.4 (1110)50.0 (767)40.22 (33.14)
21. Sore throats70.9 (1087)47.2 (724)38.92 (33.55)
22. Muscle twitching68.1 (1045)40.9 (627)35.12 (32.38)
23. Night sweats and chills67.7 (1038)46.9 (720)38.48 (34.69)
24. Sore eyes67.0 (1028)49.0 (752)39.91 (35.70)
25. Nerve pain  63.3 (971)48.8 (748)40.65 (38.16)
26. Sore lymph nodes  62.9 (965)44.0 (675)36.36 (35.28)
27. Nausea  62.2 (954)38.1 (584)31.89 (32.13)
28. Tinnitus  60.3 (925)39.8 (611)37.42 (38.96)
29. Trouble breathing  57.8 (887)40.9 (628)33.97 (35.67)
30. Neurological symptoms  57.0 (875)42.8 (656)34.60 (36.14)
31. Excessive sleep  54.4 (835)44.5 (682)36.23 (38.58)
32. Loss of appetite  49.0 (752)30.9 (474)25.41 (31.62)
33. Migraines  46.2 (708)24.6 (378)21.92 (29.27)
34. Cardiac pain and/or arrhythmia  41.2 (632)24.8 (381)21.12 (30.30)
35. Brain twangs  29.9 (459)17.7 (272)15.00 (26.82)
36. Severe burning sensation all over skin  29.7 (456)18.3 (280)15.96 (28.87)
37. Paralysis/inability to move  29.4 (451)9.4 (144)11.49 (21.91)
38. Premenstrual symptoms  21.1 (323)16.4 (251)13.56 (29.25)
39. Decreased heart rate  15.1 (231)7.4 (114)  6.88 (19.09)
Note: % endorsed “yes” means they responded yes to experiencing symptom at any level. % endorsed at “2” threshold means that they experience the symptom at least half the time. Means reflect frequency only (0–100 scale).
Table 5. If you go beyond your energy limits by engaging in pre-illness tolerated exercise or activities of daily living, do you experience any of the following? (N = 1534).
Table 5. If you go beyond your energy limits by engaging in pre-illness tolerated exercise or activities of daily living, do you experience any of the following? (N = 1534).
Items% (n)
An onset that is immediate or delayed by hours or days98.5 (1511)
Post-exertional exhaustion98.3 (1508)
A loss of functional capacity and/or stamina98.2 (1506)
Symptom exacerbation98.1 (1505)
A severity and duration of symptoms that are out of proportion to the initial trigger97.4 (1494)
An abnormal response to minimal amounts of physical and/or cognitive exertion97.3 (1492)
Substantial reduction in pre-illness activity level96.9 (1486)
A prolonged recovery that can last days, weeks, or months96.2 (1475)
Global worsening of multi-systemic symptoms94.0 (1442)
Prolonged worsening of symptoms92.9 (1425)
Table 6. Duration of PEM, illness course, and functioning (N = 1534).
Table 6. Duration of PEM, illness course, and functioning (N = 1534).
Items% (n)
Length of prolonged, unpredictable recovery period95.2 (1460)
Within 24 h14.1 (216)
Between 1 and 2 days38.9 (596)
Between 3 and 6 days58.0 (890)
Between 1 week and 1 month46.7 (717)
Between 1 and 6 months30.3 (465)
Between 6 months and 1 year13.6 (209)
Between 1 and 2 years9.8 (151)
Over 2 years12.3 (189)
Crash that has never resolved67.1 (1029)
Severity and duration out-of-proportion to the TYPE of exertion96.0 (1473)
All of the time59.0 (905)
Most of the time26.1 (401)
About half the time8.7 (133)
A little of the time2.0 (31)
Severity and duration out-of-proportion to the INTENSITY of exertion94.8 (1454)
All of the time59.5 (913)
Most of the time26.5 (406)
About half the time6.6 (102)
A little of the time1.9 (29)
Severity and duration out-of-proportion to the DURATION of exertion90.4 (1386)
All of the time56.9 (873)
Most of the time25.6 (393)
About half the time5.1 (78)
A little of the time1.8 (28)
Severity and duration out-of-proportion to the FREQUENCY of exertion84.9 (1302)
All of the time51.5 (790)
Most of the time24.8 (380)
About half the time5.5 (85)
A little of the time2.6 (40)
Adrenaline surges during or after going beyond energy limit57.2 (878)
Length of adrenaline surge before crashing *
A few minutes13.0 (200)
A few hours35.8 (549)
About 24 h16.5 (253)
Less than a week6.1 (94)
About 1 week1.3 (20)
Over 1 week1.3 (20)
How long ago did your problem with ME/CFS begin?
6–11 months ago0.6 (9)
1–2 years ago2.9 (45)
3–5 years ago12.1 (186)
6–10 years ago15.9 (244)
Over 10 years ago53.7 (823)
Since childhood/adolescence14.8 (227)
Has your illness been present for more than 50% of the time since you became ill?97.1 (1489)
How would you describe the course of your illness?
Constantly getting worse29.3 (450)
Constantly improving1.4 (22)
Persisting (no change)15.4 (237)
Relapsing and remitting7.4 (113)
Fluctuating46.2 (708)
Which statement best describes your illness over the last 6 months?
I can do all work or family responsibilities without any problems with my energy0.1 (2)
I can work full-time/finish some family responsibilities, but I have no energy left2.6 (40)
I can work full-time, but I have no energy left for anything else4.6 (71)
I can only work part-time at work or on some family responsibilities14.9 (228)
I can do light housework, but I cannot work part-time43.0 (659)
I can walk around the house, but I cannot do light housework29.9 (459)
I am not able to work or do anything, I am bedridden/completely incapacitated4.8 (73)
Pacing allows me to completely avoid symptom exacerbation6.0 (92)
Pacing allows me to avoid symptom exacerbation only to a certain degree87.7 (1345)
How frequently is pacing effective?
All the time2.3 (35)
Most of the time22.8 (350)
About half the time34.1 (523)
A little of the time27.8 (427)
How effective is pacing in reducing the level of severity of symptoms?
Very effective7.6 (117)
Moderately effective37.2 (570)
Mildly effective34.2 (525)
Barely effective8.2 (126)
If you are pacing, is it:
Based on body symptoms and reactions to triggers87.1 (1336)
With a heart rate monitor10.7 (164)
Both of the above17.3 (265)
Note: * For these items, participants could select more than one answer. There is also an option for participants to describe pacing techniques not listed.

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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