Most patients suffer with fibromyalgia for years before it is diagnosed. There are no diagnostic laboratory or imaging tests available for this disorder, and many physicians are not adequately informed or educated about it. Because there is no lasting tissue damage, fibromyalgia cannot be evaluated by the classical medical model, which uses degree of tissue damage for evaluation. Diagnosis and treatment are usually frustrating for the physician and the patient.

Medical history and physical examination are the keys for making the diagnosis. The American College of Rheumatology (ACR) has established criteria for fibromyalgia diagnosis in adults:

• Widespread pain in all four body quadrants. Pain must exist on the left and the right sides, and above and below the waist, and must persist for at least three months.
  
  
• Manual tender point survey (at least 11 of the 18 specified trigger points). A site is considered a tender point only if the individual feels pain upon the application of 4 kilograms (about 9 pounds) of pressure. Physicians may be trained to recognize “the feel” of this amount of force when applying pressure by finger.

There are different criteria for diagnosing fibromyalgia in children:

• Widespread pain in three sites without any other underlying cause lasting at least three months.
  
  
• Presence of five to 11 trigger points, which may be identified at less than 4 kilograms of pressure. Some researchers have suggested a standard of 3 kilograms (about 7 pounds) of pressure for children.
  
  
• Between three to 10 other major criteria. These criteria include:
  
  
• Chronic anxiety or tension
  
  
• Fatigue
  
  
• Poor sleep
  
  
• Chronic headaches
  
  
• Irritable bowel syndrome
  
  
• Soft-tissue swelling
  
  
• Numbness
  
  
• Pain varies with physical activity (more than with adult fibromyalgia)
  
  
• Pain varies with weather conditions (less than with adult fibromyalgia)
  
  
• Pain varies with anxiety and stress (less than with adult fibromyalgia)

These criteria do not have to be noted all in one examination but can be recorded over time.

In addition to the ACR criteria mentioned above, doctors rely upon thorough patient medical histories, patient-reported symptoms, clinical or physical examination, pain assessment forms and routine tests to help exclude certain other conditions with similar symptoms. Many conditions that mimic the symptoms of fibromyalgia must be ruled out. However, the presence of other diseases does not eliminate the possibility of a diagnosis of fibromyalgia. Conditions that may be tested for include:

• Polymyalgia rheumatica. An episodic, chronic, inflammatory condition primarily affecting individuals over the age of 50. It is characterized by muscle stiffness and pain within the shoulders, hips, or other regions and is frequently associated with inflammation of certain large arteries. Fibromyalgia does not involve inflammation. A blood test may be used to verify the presence or absence of polymyalgia rheumatica.
  
  
• Osteoarthritis. A generally noninflammatory degenerative joint disease common in older individuals. It is marked by stiffness, tenderness, pain and potential deformity of affected joints. Fibromyalgia does not involve deformity but may coexist with osteoarthritis. Imaging tests may be used to diagnose osteoarthritis.
  
  
• Ankylosing spondylitis. A chronic, progressive, inflammatory disease primarily involving joints of the spine and leading to stiffness, pain and potential loss of spinal mobility. Fibromyalgia does not involve inflammation or loss of spinal mobility. A diagnosis of ankylosing spondylitis may involve imaging tests.
  
  
• Rheumatoid arthritis. A chronic disease primarily characterized by persistent inflammation of joints, resulting in discomfort, pain, swelling and potential deformity of the affected joints. Fibromyalgia does not involve inflammation or deformity but may exist with rheumatoid arthritis. A diagnosis of rheumatoid arthritis may involve blood and imaging tests.
  
  
• Systemic lupus erythematosus (SLE). A chronic, inflammatory disorder that can involve many parts of the body, including joints, skin and kidneys. Fibromyalgia is not inflammatory but may exist with SLE. Blood and imaging tests may be used in the diagnosis of SLE.

Although there are no specific tests for fibromyalgia, certain abnormalities may be detected through blood tests, spinal tap or imaging tests. Levels of substance P (responsible for initiating pain signals) are high in the brain and spinal fluids, whereas levels of serotonin (responsible for reducing pain intensity) and growth hormone (responsible for building muscle) are low. These tests are not sensitive and specific for the disease and not commonly performed. Blood flow to the thalamus region of the brain is also low. Brain wave levels are high at night and low during the day. Normal findings in the levels of many blood chemicals may be used to eliminate other possible conditions.

Once fibromyalgia is diagnosed, physicians may require formal or informal assessments to detect potential mood disturbances such as depression and anxiety, and a sleep history including investigation into possible disturbances such as restless leg syndrome or sleep apnea.