A myriad of diagnostic tests have been studied for CRPS. Bone scans may be normal or show increased or decreased uptake in CRPS.⁹² (See Figure 9.) The bone scan also suffers from the subjective interpretation of the radiologist. Furthermore, researchers disagree on its adequacy, specificity, and sensitivity.^{93, 94} Tourniquet ischemia test appears to produce a progressive blockade of nerve transmission, but the interpretation of this test is under intense scrutiny. Plain radiographs help rule out issues such as fractures, which may be responsible for the symptoms, but for CRPS there are no radiographic changes or evidence of osteoporosis in the acute phase.⁹⁵ Radiographic demineralization may be noted in the later phase of CRPS using X-rays when comparing the affected area with a normal area, however this is also noted with disuse or immobilization of the limb. Other tests like EMG’s, laser Doppler, and microneuronographic measurement of peripheral sympathetic function also have not yet proven their utility.⁹⁶ MRI may show nonspecific soft tissue changes.⁹⁷ Sympathetic nerve blocks were once considered diagnostic for CRPS type I, however they are not entirely reliable, reproducible, easy to interpret, and they lack specificity.⁹⁸ There is also a problem of placebo effect and false-positive results. The diagnosis therefore of CRPS is one of exclusion, with these tests being used as an aid to the total clinical picture.⁹⁹ Clinical assessment remains the gold standard of diagnosis of CRPS.¹⁰⁰

Figure 9. Bone scan of knees. In this bone scan, increased uptake can easily be seen in the right knee. This patient was diagnosed with CRPS.

The physician should take a detailed medical history considering an initial trauma and any history of sensory, autonomic and motor disturbances. The clinician should ask for the development, time course, distribution and characteristics of pain. A general neurological examination is needed. Detection of any swelling, sweating, trophic, temperature and motor abnormality in the disturbed area is important. Muscle strength of the affected limb, as well as characteristics and distribution of somatosensory abnormalities should be investigated in detail. The physician should also test whether the pain can be elicited by movements and pressure at the joints.¹⁰¹ If the ligaments or soft tissues are still traumatized, stressing them by motion or pressure will elicit sharp pain. This can be documented with a dolorimeter. (See Figure 10.)

Figure 10. Dolorimeter pressure assessment. A dolorimeter measures the amount of pressure required to elicit pain at a specific location. Less pressure is needed to elicit pain at the ligaments in the CRPS patient.

Essential to the diagnosis is the presence of some initiating event and/or cause of immobilization.¹⁰² The clinical picture includes continuing pain that is out of proportion to the event which caused it; sensory changes such as hyperesthesia; autonomic abnormalities such as changes in skin blood flow, or abnormal sweating at the site of pain, and swelling or edema which is typically peripheral, and may come and go; trophic changes of the skin and appendages; and motor dysfunction such as weakness of the muscles.^103-106 It is also necessary to exclude other conditions that may account for the pain or symptoms.