Differential diagnosis

Differential diagnosis is the process which tries to make a correct diagnosis by excluding other diseases which can cause similar symptoms.

ME/CFS
Many diseases can cause similar symptoms ME/CFS: However, if strict diagnostic criteria and diagnostic testing for other conditions is used, misdiagnosing a patient suffering from the conditions above with ME/CFS is unlikely.
 * infectious diseases (such as Epstein–Barr virus, influenza, HIV infection, tuberculosis, Lyme disease)
 * neuroendocrine diseases (such as Hashimoto's thyroiditis (hypothyroidism), 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 depression, 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 such as lupus or rheumatoid arthritis, some other chronic illness, alcohol or substance abuse, pharmacologic side effects, heavy metal exposure and toxicity, marked body weight fluctuation)

There are however some diseases, which can mimic ME/CFS. Some presentations of these illnesses could meet even the most strict ME/CFS diagnostic criteria (CCC and ICC), resulting in patients being wrongly diagnosed with ME/CFS, whilst suffering from something else. These will be discussed in detail below.

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

Spinal Stenosis
A case report of three patients, all having being diagnosed with ME/CFS and presenting with classic symptoms such as: PEM, POTS, sleep and cognitive problems, etc. found that all three had been misdiagnosed with ME/CFS. The real cause of their symptoms was spinal stenosis, which was compressing the spinal cord. After surgery all three patients recovered. One of the patients even went from house bound to working 12 hour shifts on a regular basis. Furthermore, one of the patients had a sudden onset, caused by a viral infection, a sign typically associated with ME / CFS.

Idiopathic Intracranial Hypertension
There is a lot of overlap between symptoms of IIH and ME/CFS. Headache is a common in ME/CFS patients and is a classic symptom in IIH. A study of patients diagnosed with ME/CFS, where most of the participants had headache as a symptom found that 20% met the diagnostic criteria for intracranial hypertension.

Chiari Malformation
Chiari malformation, is a structural deformity, where a part of the brain stem is out of its normal position. This disease can present with many neurologic symptoms that very similar to ME/CFS and should be excluded. Usually this is done via MRI scan. There was one report however of a missed Chiari problem, that was only visible in a MRI scan in the standing position.

Craniocervical Instability
Craniocervical instability is another structural problem, where the tendons that connect the base of the skull with the spinal cord are loose, causing brain stem compression, which in turn causes many neurologic symptoms similar to ME/CFS. Several anecdotal reports of complete recovery following CCI surgery have been posted on ME/CFS support forums. However it is yet to be determined how common this issue is with ME/CFS patients.