Recently A.M. asked: “when severe anxiety disorder is present, can you distinguish Chronic Fatigue Syndrome because the symptoms are so similar?”

The answer is, “It may be difficult.” However, there are characteristics that tend to differentiate the two:
(1) Anxiety tends to be more of a lifelong disorder, whereas ME/CFS more frequently has a more distinct and recent onset. (2) Anxiety frequently responds modestly to medication such as benzodiazepines, while ME/CFS does not. (3) The severity of symptoms such as pain, fatigue, non-restorative sleep, and upright intolerance are more severe in ME/CFS whereas “worry” tends to be more severe in anxiety.(4) Anxiety is not usually associated with the symptoms of recurrent fever, sore throat, and swollen glands. (5) Anxiety tends to paralyze the patient with symptoms, who may be withdrawn, whereas persons with ME/CFS are pro-active but exhausted.

From a biochemical standpoint, we would see low white cell and Natural Killer Cell counts, elevated LDL levels, low IgG, elevated CD8/CD38 cells, possibly a higher prevalence of DR3, DR4, DQ1 and DQ3 alleles, abnormal MRIs, and distinctive QEEGs or SPECT scans in persons with ME/CFS.

So you see, a careful history and examination can help discriminate the two. I hope this helps!