Myalgic Encephalomyelitis/Chronic Fatigue Syndrome and Fibromyalgia: Definitions, Similarities, and Differences

Abstract

This commentary presents a simplified way of making the diagnosis of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) using the 1994 Centers for Disease Control and Prevention case definition. The format used can easily be modified for other case definitions. The commentary then discusses whether ME/CFS is the same or a different illness from fibromyalgia. Because overlap exists between the 2 syndromes, some investigators have posited that they are variants of the same illness. I have viewed this as an empirically testable hypothesis and have summoned considerable amounts of data that suggest that the 2 illnesses differ. Were differences to exist, that would suggest different pathophysiologic processes for each, leading to different treatments.

Keywords: fatigue; overlap; pain; unexplained illness.

Figure 1.

Visual analog scale shown to patients during their evaluation for the possible diagnosis of CFS. To use this most efficiently, put this on one side and Figure 2 on the back side of a piece of paper.

Figure 2:

Read this script to the patient. If the patient fulfills the criteria noted herein, that patient will fulfill the 1994 CDC case definition for CFS. If the patient reports problems with unrefreshing sleep, cognitive problems and post-exertional malaise, the patient would also fulfill criteria for the 2015 clinical case definition developed by an expert committee at the IOM.

Figure 3:

This figure depicts the location of the 18 tender points that should be probed for tenderness at a force of 4 kg. Usually the patient will report pain at substantially less pressure than 4 kg. If the patient reports tenderness at more than 10 of the 18 locations, that fulfills the tender point requirement for the diagnosis of FM.

Figure 4:

This figure shows a summary of all the transitions among sleep stages for CFS only, CFS+FM and healthy controls. Note that the sleep architecture of the CFS only patients differs considerably from those with CFS+FM.