In the past fibromyalgia was called 'fibrositis' and Chronic Fatigue Syndrome has now replaced the terms 'chronic mononucleosis' and 'chronic Epstein-Barr syndrome'. In Victorian times CFS was probably known as 'neurasthenia' and 'nervous exhaustion'.

For many people the diagnosis CFS and FMS seems to be interchangeable. However, there are certain symptoms like fever and swollen glands that are found in a higher percentage in CFS patients than those with FMS.

One similarity is in age and gender. The majority of diagnosed cases of CFS occur in women, most of whom are 25 to 45 years old. FMS strikes mostly women between the ages of 20 and 50.

Prevalence of CFS

Two studies using the same working definition and including a medical work-up have estimated the prevalence to be approximately 200 per100,000 of the general population. (1) In Japan, a study found that the proportion of CFS cases was 14.8% for both sexes, and tended to be slightly higher among females than males. There was no relation to age. (2)

According to the Centers for Disease Control, the "...minimum prevalence rates for the period 1 September 1989 to 1 September 1991 ranged from 2.0 to 7.3 per 100,000 of the general population..... More than 80% of the CFS cases were female, most were white, and their average age at onset was approximately 30 years. (3)

Prevalence of FMS

A British study calculated annual incidence of fibromyalgia in females was 583 per 100,000. (4) In the US the prevalence of fibromyalgia according to a 1995 study was 2.0% for both sexes, 3.4% for women, and 0.5% for men. (5)

Main Complaint

The main complaint in Chronic Fatigue Syndrome (CFS) is the extreme and around-the- clock fatigue. The smallest physical exertion can totally deplete a person confining the person to bed for days. There is no official clinical test to diagnose CFS. Instead, doctors rule out other diseases before making a Chronic Fatigue Syndrome diagnosis.

Fibromyalgia, on the other hand, is an arthritis-related condition. The primary complaint is round-the-clock pain that rarely goes away. In contrast to CFS, FMS can be diagnosed according to the criteria set forth by the American College Rheumatology.

Common Symptoms

In a 1990 conference on CFS and FMS in 1990 Carol Jessop MD (6) gave the following symptoms has beeing common in both conditions. These findings are from seeing thousands of patients in her practice.

100% of the patients with FMS have muscle pain as part of their symptom picture. Part of the diagnosis is finding 11 out of 18 tender points. On the other hand, many CFS patients do not have enough tender points to satisfy the standard criteria for fibromyalgia.

Also, irritable bowel syndrome is probably more common in FMS.

Physical Findings

Dr. Jessop in her practice found the following common physical findings between CFS and FMS. The data is from 1,324 patients of which 75% were female.

Cognitive Impairment

The difference in cognitive impairment between CFS and FMS is one of degree. Overall, cognitive impairment is less debilitating in FMS than in CFS. The following table lists the different percentages in cognitive impairment between the two. (7)

CFS	%	FMS	%
forgetfulness excessive irritability confusion difficulty thinking poor concentration	79 63 58 67 79	forgetfullness excessive irritability confusion difficulty thinking poor concentration	21 17 13 17 33

REFERENCES

2. J Epidemiol 1996 Jun;6(2):75-80 Descriptive epidemiology of chronic fatigue syndrome based on a nationwide survey in Japan Minowa M, Jiamo M

3. Ciba Found Symp 1993;173:83-93 Epidemiology of chronic fatigue syndrome: the Centers for Disease Control Study.

4. Br J Rheumatol 1997 Dec;36(12):1318-1323 A population study of the incidence of fibromyalgia among women aged 26-55 yr. Forseth KO, Gran JT, Husby G

5. The prevalence and characteristics of fibromyalgia in the general population. Wolfe F; Ross K; Anderson J; Russell IJ; Hebert L Arthritis Rheum, 38(1):19-28 1995 Jan

6. Fibromyalgia Network Newsletters : October ‘90 thru January ‘92 Compendium #2, January 1993, May 1993 Compendium, January 1994, July 1994. Available from Fibromyalgia Network 5700 Stockdale Hwy, Suite 100,Bakersfield, CA 93309-2554 USA

7. Yunus MB, Masi AT, Calabro JJ, et al: Primary fibromyalgia (fibrositis): clinical study of 50 patients with matched normal controls. Semin Arthritis Rheum 11:151-157, 1981