Differential diagnosis

Differential diagnosis is the process which tries to make a correct diagnosis by excluding other diseases which can cause similar symptoms. Many diseases can cause similar symptoms to CFS / ME: However, if strict diagnostic criteria is used, misdiagnosing a patient suffering from the conditions above with CFS / ME is unlikely. There are however some diseases, which can mimic CFS / ME. Some presentations of these illnesses could meet even the most strict ME / CFS diagnostic criteria (ICC), resulting in patients being wrongly diagnosed with ME / CFS, whilst suffering from something else.
 * infectious diseases (such as Epstein–Barr virus, influenza, HIV infection, tuberculosis, Lyme disease)
 * neuroendocrine diseases (such as thyroiditis, Addison's disease, adrenal insufficiency, Cushing's disease)
 * hematologic diseases (such as occult malignancy, lymphoma)
 * rheumatologic diseases (such as fibromyalgia, polymyalgia rheumatica, Sjögren's syndrome, giant-cell arteritis, polymyositis, dermatomyositis)
 * psychiatric diseases (such as bipolar disorder, schizophrenia, delusional disorders, dementia, anorexia/bulimia nervosa)
 * neuropsychologic diseases (such as obstructive sleep apnea, parkinsonism, multiple sclerosis)
 * others (such as nasal obstruction from allergies, sinusitis, anatomic obstruction, autoimmune diseases, some chronic illness, alcohol or substance abuse, pharmacologic side effects, heavy metal exposure and toxicity, marked body weight fluctuation)

Multiple Sclerosis
Neurological symptoms, such as POTS and dysautonomia are very common in CFS / ME patients, those same symptoms are common in M.S. as well. Furthermore M.S. can often present with fatigue.