Home Diagnosis



"The pattern of symptoms is unique, there is no other illness in general medical practice that looks like this one."

— David Bell, M.D.

CFIDS researcher

photo of a woman with her hand against her head
Diagnosis PDF Print E-mail

Before Diagnosis

Suppose you have been sick with an ongoing flu-like illness that has lasted weeks or months. The sickness and fatigue are overwhelming. Then you feel a bit better after many days in bed, only to get sicker within a short period of time when you try to function.


The fatigue you experience is also quite unusual. Especially unusual is the fact you feel more prostrated the day after you do something rather than the day you do it. (It's the "run over by a Mack truck" or having been "beaten up" feeling.) You have to go to bed for at least a day and virtually not move in order to sort of recover. Unless you have had mononucleosis, or some other type of extremely fatiguing similar illness, you have never experienced anything like this — nor for as long. What happens next?


If the physician you see knows you, s/he may know there is a new and different illness present, but may not really know what it is. The doctor does some lab tests, but says the tests are more or less normal. A couple of specialists may be consulted, who again aren't offering anything definite—or they may concentrate on one or two symptoms without assessing the overall picture. It is common for patients like you to see many doctors over months or occasionally up to a few years, before getting a definite diagnosis.

At the time of this writing, while much has been learned about CFS/CFIDS/ME and how to identify this illness, there is no definitive biological marker.

Why an Accurate Diagnosis is Important

  • To be sick and not know what the problem is makes it impossible to know what is happening. It is like being lost without a map.
  • By identifying the illness, the patient will know what treatments are available and how to obtain help in coping with CFS/CFIDS/ME or FM.


The most immediate and ongoing experience with the Chronic Fatigue Syndrome/Chronic Fatigue and Immune Dysfunction Syndrome/Myalgic Encephalopathy/Myalgic Encephalomyelitis (CFS/CFIDS/ME) and Fibromyalgia (FM) are their symptoms. Unlike many other illnesses, both have many different symptoms that may change from day to day, week to week, and month to month. Although FM is diagnosed solely on the presences of pain criteria, it shares many of the same symptoms of CFS/CFIDS/ME in various patients. Identification of an ongoing and coherent pattern and clustering of symptoms is one element in making a diagnosis. As a patient, it is very helpful to see and understand that the number and types and symptoms that you have are, in fact, common to other patients with CFS/CFIDS/ME and FM.


Here is an extensive list of CFS/CFIDS/ME symptoms (many of which also frequently occur in FM patients) which has been drawn up by several international experts on the illness.

Most Common CFS/CFIDS/ME Symptoms

  • Exhaustion, made worse by physical exercise (100%)
  • Low-grade fever in early stages (60-95%)
  • Recurrent flu-like illness (75%)
  • Frequent pharyngitis (sore throats) (50-75%)
  • Joint and muscle pain (65%)
  • Severe muscle weakness (40-70%)
  • Stiffness (50-60%)
  • Post-exertional fatigue & flu-like symptoms (50-60%)
  • Multiple sensitivities to medicines, foods, and chemicals (40-60%)
  • Severe nasal & other allergies (often with worsening of previous mild allergies) (40-60%)
  • Frequently recurring, difficult to treat respiratory infections (40-60%)
  • Dyspnea (labored breathing or hunger for air) on exertion
  • Painful lymph nodes (especially in the neck and under arms) (30-40%)

Neurological Symptoms

  • Sleep disorders & unrefreshing sleep (50-90%)
  • Headaches (35-85%)
  • Visual blurring (50-60%)
  • Intolerance of bright lights
  • Parasthesias (numbness or tingling feelings) (30-50%)
  • Dizziness/ Lightheadedness (30-50%)
  • Ringing in the ears
  • Impaired cognition (50-85%), which may include:
    • Attentional difficulties
    • Calculation difficulties
    • Memory disturbance
    • Spatial disorientation
    • Saying the wrong word

Other Symptoms

  • Worsening of premenstrual symptoms (70% of women)
  • Nocturia (excessive urination during the night) (50-60%)
  • Tachycardia (abnormal rapid heart action) (40-50%)
  • Chest pain (25-40%)
  • Cough (30-40%)
  • Weight gain (50-70%)
  • Nausea, especially in earlier stages (50-60%)
  • Diarrhea, intestinal gas or irritable bowel (50%)
  • Intolerance of alcohol
  • Night sweats (30-50%)
  • Dry eyes (30-40%)
  • Dry mouth (30-40%)
  • Rash (30-40%)
  • Frequent canker sores (30-40%)
  • Herpes simplex or shingles (20%)
  • Symptoms worsened by extremes in temperature

(Statistics compiled from data on CFS patients by: Paul Cheney MD, Anthony Komaroff MD, Charles Lapp MD, Daniel Peterson MD)


CFS/CFIDS/ME Is A Serious, Usually Chronic, Multi-systemic, Physical Illness

Despite what you may have heard or been told, it is essential to know that CFS/CFIDS/ME is a real and serious physical illness.


The international medical researchers and clinicians who have done the best and most rigorous scientific work and treated thousands of patients are in full agreement that the illness is organic and not psychologically caused. It involves pathology in multiple systems of the body including: the immune system, the neurological system including the brain, the endocrine system, the cardiovascular system, as well as other systems and organs. There is a consensus that viruses, either new or latent, are frequently involved, but other factors have been implicated as triggers, such as exposure to pesticides or other chemicals.


CFIDS/CFS/ME is currently defined as a syndrome—that is, an illness that is characterized by a coherent and specific pattern of symptoms that does not occur in other illnesses. Currently there is no clear known cause, but there are known disturbances to important body systems that clearly contribute the existence of the symptoms.


What is Necessary to Receive a Correct and Accurate Diagnosis of An Illness?

Before any illness can be diagnosed, medical science must provide an accurate "case definition" for the illness—a definition that correctly describes the signs, symptoms, illness progression, pathophysiology (deleterious effects of the illness on the body), laboratory abnormalities, and known causal agents. Second, this "case definition" must distinguish the specific illness from other known illnesses—otherwise a specific illness would not be distinguishable from other illnesses, and a diagnosis of it would be impossible.


The preceding discussion is necessary because there has been much confusion and disagreement as to what the illness CFIDS/CFS/ME actually is. Not only is the illness known by various names: Chronic Fatigue Syndrome (CFS), Chronic Fatigue Immune Dysfunction Syndrome (CFIDS), Myalgic Encephalopathy and Myalgic Encephalomyelitis (ME), but there are several different case definitions that describe the illness somewhat differently and provide different diagnostic criteria. Because the illness first became widely identified in the mid-1980s, a number of case definitions and diagnostic criteria were developed as physicians and researchers learned more about the illness.


Therefore patients and physicians would benefit from knowing which case definitions and diagnostic criteria for the actual illness are the most scientifically and medically accurate.


In order to obtain a diagnosis of CFS/CFIDS/ME, the patient must see a physician who is sufficiently knowledgeable to evaluate the illness according to CFS/CFIDS/ME diagnostic criteria. We feel the 2003 Canadian definition is the most accurate of the various criteria sets available.


If one has Fibromyalgia (FM), the situation is more fortunate in terms of diagnostic criteria. The 1990 U.S. College of Rheumatology diagnostic criteria are short and straightforward:

  • Widespread pain for at least 3 months.
  • Pain in all four quadrants of the body: right side, left side, above and below the waist.
  • Pain in at least 11 of 18 specified tender points when they are pressed. These 18 sites cluster around the neck, shoulder, chest, hip, knee, and elbow regions.

No exclusions are made for the presence of concomitant radiographic or laboratory abnormalities.



General Diagnostic Schema for CFS/CFIDS/ME Under The Various Case Definitions

It is important to know the overall, step-by-step method by which CFS/CFIDS/ME is diagnosed under any of the definitions. It is a careful and rigorous approach. Beware of any physician who does not follow it and makes a diagnosis in a more casual or shortcut manner. One example would be if a patient was simply fatigued and had higher than average Epstein-Barr virus antibody titers, and was given a diagnosis on that basis alone.


First, the diagnosis of CFS/CFIDS/ME must be a process of exclusion—the initial step is to make sure that some other known illness is not causing the patient's symptoms and disease. CFS/CFIDS/ME has a coherent and identifiable set of symptom-complexes and pathophysiological effects on the body, but there is as yet no one cause that can be clinically identified, and there is as yet no available set of laboratory tests that can distinguish CFS/CFIDS/ME from any other illness.


As a result, CFS/CFIDS/ME is only identifiable by its coherent symptom-complex when other illnesses have been excluded. Once similar-looking illnesses have been ruled out, CFS/CFIDS/ME is recognizable enough that it can be diagnosed with reasonable confidence.


The major illnesses and conditions that have some or many symptoms similar to CFS/CFIDS/ME must be ruled out, not only to identify the CFS/CFIDS/ME, but also to detect whether another illness is in fact present. A number of these other illnesses are serious in nature and require immediate diagnosis and proper treatment. Each of the major diagnostic case definitions lists many of these exclusionary illnesses. For instance, cancer, myasthenia gravis, lupus, endocrine diseases, Lyme disease, and major biological depression can be misinterpreted as CFS/CFIDS/ME without proper exclusion.


Please note: For those people who already have CFS/CFIDS/ME, if new symptoms develop during the course of the illness, don't just assume that they are new or variant symptoms of CFS/CFIDS/ME. People with this illness can develop new illnesses that require diagnosis and treatment. So, if new symptoms are present, err on the side of caution and see a physician to rule out another illness. If s/he seems unnecessarily casual about it, seek a second opinion.


As part of the patient evaluation, both to exclude other illnesses and to identify the characteristic CFS/CFIDS/ME symptom-complex, the physician will:


1. Evaluate the patient's current illness state, which includes identification of symptoms, illness status, circumstances of onset and progression since onset. This step also includes appropriate physical examination as determined by symptoms and the patient's account of current illness and onset. The various diagnostic criteria will give more detail on this phase.


2. Take a Patient History: The examining physician should also take a thorough patient history in the effort to explore elements of the history that might shed light on the current illness.


3. Do laboratory and other testing: Such testing as described in the diagnostic criteria is done to rule out other likely differential diagnoses. Also, these tests, upon careful review (see diagnostic criteria and research findings elsewhere) may aid in providing confirmation to the identification of CFS/CFIDS/ME by symptom-complex.


Once there are no other active illnesses identified (or current illnesses under successful treatment) which would explain the current symptoms, the second major phase of the diagnostic process is to apply a Case Definition of CFS/CFIDS/ME in order to determine whether the patient's illness and symptoms meets the standard of the specific diagnostic criteria.


The major case definitions of CFS/CFIDS/ME contain a listing of what may be co-morbid or non-exclusionary diagnoses; that is, other diagnoses that are permitted to accompany a CFS/CFIDS/ME diagnosis. In fact, some of these diagnoses may be expected to accompany a CFS/CFIDS/ME diagnosis, including fibromyalgia (FM), an overlapping, but separate illness process found in 80% of CFS/CFIDS/ME patients. Also, diagnoses of secondary anxiety or depression are not uncommon with CFS/CFIDS/ME, as they are not uncommon in many other chronic physical illnesses.


It is even possible for a person meeting the CFS/CFIDS/ME case definition to simultaneously have a primary depressive process, just as a person with primary depression can develop any other illness. However, for most CFS/CFIDS/ME patients, anxiety and/or depression are secondary to having CFS/CFIDS/ME.  This is true also for Fibromyalgia. That is one reason for the taking of a careful medical history.


Diagnosis of Fibromyalgia (FM)

The 1990 U.S. College of Rheumatology diagnostic criteria are straightforward:

  • Widespread pain for at least 3 months.



Finding a Physician to Make a Proper and Accurate Diagnosis of CFS/CFIDS/ME

To obtain a proper and accurate diagnosis of CFS/CFIDS/ME, patients must have a physician who is sufficiently informed about the illness to make a proper and accurate diagnosis. Ideally s/he must be familiar enough with the 2003 Canadian and the current CDC definitions to apply them capably and correctly. So not only must the physician be able to diagnose CFS/CFIDS/ME, s/he must be a good diagnostician in terms of making differential diagnoses of neurological, endocrine, cardiovascular, and in some cases, psychiatric illness. Hence, a general practitioner may wish to consult one or more specialists.


Because CFS/CFIDS/ME is an illness about which physicians are still not sufficiently educated, patients must try to educate themselves to decrease the chances of misdiagnosis.


Occasionally the physician may be fairly well informed about CFS/CFIDS/ME and about how to diagnose the illness. In this case, the patient may be able to receive a proper diagnosis within a reasonable period of time. Unfortunately, experience shows that many doctors, both primary care physicians (PCPs) and specialists, are not yet well-informed about the illness, and so obtaining a diagnosis may take longer and be more difficult. The same is true about treatment/management; that is, the physician may be able to diagnose CFS/CFIDS/ME yet not know how to manage it.


Many PCPs will be open-minded and will be willing to learn about the illness, especially if the physician knew the patient as a healthy person. In this case, the patient can give the doctor the 2003 Canadian and/or the current CDC definition (based on the 1994 definition), along with a few other medical or informational articles. The patient must be selective in the amount of material s/he gives to the doctor, since doctors are busy. The doctor may consult with a colleague who knows more about the illness. If a PCP is confident in his or her ability to learn about the illness, s/he may make at least a tentative diagnosis of CFS/CFIDS/ME. If the doctor expresses uncertainty about knowing enough about CFS/CFIDS/ME for diagnosing, or seems unwilling to learn more about it, then request a referral to a physician more informed about the illness.


A specialist who is unfamiliar with CFS/CFIDS/ME can make a misdiagnosis as well as any other physician. Such misdiagnoses can often lead to many months of difficulty and, perhaps, improper treatment. To the extent possible, it is best to avoid these discouraging and painful detours that result from misdiagnosis. (Please see the section on Differential Diagnoses, and don't be shy in providing the linked articles or printouts to either a PCP or specialist, if appropriate.)


What To Do If A Doctor Insists "Nothing" Is Wrong

Unfortunately, some patients have found that a previously concerned, friendly and helpful PCP may be less than helpful with a CFS/CFIDS/ME diagnostic process. The same can occur with any other doctor. After an initial work-up, the PCP may say that s/he really can't find anything wrong, that the lab tests seem to be normal, and that the patient just really needs to rest, and then can resume a normal routine. The patient may try this but finds it impossible because of the continuing symptoms, goes back to the doctor and reiterates the symptoms. The doctor begins to sound like a broken record while telling the patient "there is really nothing wrong." Both the patient and doctor can become very frustrated with this process. However, the patient must be persistent in reporting the symptoms to the physician.


The doctor may become more distant and less friendly. S/he may imply the patient isn't physically ill; may state that the patient is under too much stress or have emotional problems and s/he may refer the patient to a psychiatrist. The doctor, rather than honestly expressing a lack of understanding, may begin to insist that as a doctor, s/he is in the best position to know what is going on.


Two things may be happening. First, when a doctor can't find anything physically wrong, the default clinical position is often that the illness might well be psychiatric. Second, some doctors are overly concerned about being in control. So rather than admitting they cannot determine what is wrong, they need to feel they can make an actual diagnosis. Thus if the doctor can find no "objective" evidence (other than the sick patient in front of him/her), then s/he may conclude that the illness is psychiatric or due to "stress".


If this is the case, then the patient will clearly have to find another doctor who is informed and experienced enough to make a careful and objective diagnosis.  If the patient is finally diagnosed properly—whether the diagnosis is CFS/ME or not—then the patient will have to decide whether s/he can still work with the PCP. Perhaps, after another, better-informed doctor makes the correct diagnosis, the PCP will accept the diagnosis and be willing to again engage in a genuinely helpful patient/doctor relationship.


Some patients find that their PCP is very good for routine and other medical issues, while at the same time they see a better-informed physician for CFS/CFIDS/ME treatment. However, this is not the best arrangement, since CFS/CFIDS/ME cannot be separated from the patient's overall health. Should another illness develop, only a doctor who is keeping up with the patient's entire clinical picture is in the best position to recognize a new and separate problem.


Is There A Psychiatric Illness?

One of the thornier problems in the differential diagnosis of CFS/CFIDS/ME is whether the patient has CFS/CFIDS/ME or a psychiatric illness. In some cases, there can be a genuine need to make a differential diagnosis between CFS/CFIDS/ME and a psychiatric illness. Here the most important diagnostic step to differentiate primary from secondary (post-illness) onset is the patient's history.  If not carefully and thoroughly done, the physician may miss what is a simple but very imporant differentiation.  Taking an adequate history requires more than a few minutes!


In cases where CFS/CFIDS/ME is already established, there can be difficult, sometimes very difficult, emotional problems coping with and living with this illness. There can be definite secondary depression or anxiety secondary to having to deal with the very real problems caused by the illness. A properly trained mental health professional who is knowledgeable about CFS/CFIDS/ME can be supportive and additionally help a patient figure out ways to cope with the illness. In cases in which the patient becomes severely depressed or even suicidal, then such mental health care becomes imperative, and a physician would be negligent in not making a referral.


However, there is all too often a psychiatric referral for differential diagnosis that is made out of ignorance or for biased reasons. If the PCP is making the referral because of some real question in his/her mind of whether the illness is CFS/CFIDS/ME or psychiatric, the patient must carefully consider the PCP's reasoning and explanation for the referral. If there is some genuine doubt that the patient is not physically ill or that the primary cause for physical symptoms is psychological (a rarity of cases), then proper differential diagnosis would call for a psychiatric consult—but only to a psychiatrist or psychologist who is well informed about CFS/CFIDS/ME. All too often referrals to psychiatrists and other mental health professionals result in blatant misdiagnoses that can become a harmful and counter-productive problem that will take much effort to rectify. If the patient finds a psychiatric consult to be unhelpful or "psychologically-biased" concerning physical symptoms, then the patient should leave.


Make sure to see a mental health professional who is properly informed about CFS/CFIDS/ME. An example of such an instance might be that a patient is applying for Social Security and the PCP has indicated some concern that the patient suffers from depression rather than CFS/CFIDS/ME. Then, a properly educated mental health professional would set the record straight that the patient does in fact have CFS/CFIDS/ME.

Summary of Elements Necessary to Obtain A Proper and Accurate Diagnosis of CFS/CFIDS/ME or FM

  • The patient should learn as much as possible about how a proper and accurate diagnosis of CFS/CFIDS/ME or FM is made: what medical Diagnostic Criteria are most accurate and in current use. (We recommend the 2003 Canadian definition.) The patient, his/her family and significant others must be in a position to evaluate if the physician is properly diagnosing the illnesses, or if a misdiagnosis is occurring. A patient cannot be his or her own doctor—not only is this impossible, it is hazardous—but an educated patient can assist the physician and be, as much as possible, a partner with him or her. This is difficult when the patient is very sick, so perhaps a family member or friend can help with this. Unfortunately, with so much misinformation about these illnesses, even among many fine doctors, the patient must be able to evaluate what is going on. Moreover, by being informed, the patient can provide the physician, when appropriate, with copies of the Diagnostic Criteria and other information on the illnesses. Many doctors who are not fully informed about the illnesses will appreciate receiving scientific and medical information that will assist them in diagnosing and treating their patients.


  • The patient must be able to describe his/her illness as carefully and accurately as possible to the physician—the symptoms of the illness, how severe they are, do they come and go; how did the illness begin, how does it occur from day-to-day and week-to-week. The physician needs to be able to spend the necessary time evaluating the illness and eliciting from the patient the information needed to make a careful diagnosis. It is crucial that the patient is as succinct and well-organized as possible during the visit.  This requires homework before the appointment, perhaps with the assistance of a family member or friend.  Without that preparation on the part of the patient the physician can't do his/her job.


  • The patient needs to have a doctor who is capable of making an accurate and proper diagnosis. The physician should be sufficiently informed as to the actual nature of the illness and how the proper diagnostic criteria are correctly applied.

More Resources

Dr. Byron Hyde 2012 Fall Lecture Summary

Dr. Benjamin Natelson is keynote speaker at Mass CFIDS/ME & FM Association (Spring 2012)

Dr. Gudrun Lange Reviews Neuropsychological Testing for CFS and FM (Spring 2012)

25 Year Follow-up in Chronic Fatigue Syndrome: Rising Incapacity by Dr. David Bell (Spring 2011)

Clinical Guides to Diagnosis and Treatment

CFIDS Self-Care : The Basics

Comprehensive Treatment of Fibromyalgia

Dr. Roy Freeman Describes Autonomic Nervous System Dysfunction

Genetic and Environmental Factors Impact CFS Patients

On the Morbid Fascination with Psychiatric Morbidity

The CFIDS Initiation - A Primer for New Patients

The Physical Basis of CFS

parkinDESIGN logo