There is no single test for the diagnosis of reflex sympathetic dystrophy. A doctor will ask questions about general health, family medical history, the symptoms being experienced and any history of trauma, however minor.
When a condition like RSD does not have a specific diagnostic test, sometimes the doctor just needs to make sure than no other similar condition is associated with the symptoms. In addition, RSD has a cluster of specific symptoms that, when found together, indicate the probability of the disease. The doctor will do a pinprick test to see the pain sensation and will do other test of muscle strength, range of motion of the joints and the appearance of the skin and tissue. Hot and cold can be applied to see how much those sensations are felt. One test that can be helpful is a bone scan. A bone scan can tell if there is weakness or demineralization of bone, a common phenomenon in RSD.
Types I and II Disease
In CRPS types I and II disease, the diagnostic criteria include the presence of pain with a stimulus that does not normally cause pain (a condition called allodynia) or spontaneous pain without a stimulus at all. It tends not to be limited to the area covered by a single peripheral nerve and the pain is out of proportion to whatever trauma caused the symptoms in the first place.
The two types differ only in the nature of the inciting event. Type I CRPS develops following an initiating noxious event that may or may not have been traumatic, while type II CRPS develops after a nerve injury.
Several tests can be tried to see what’s going on in cases of CRPS. These include thermography, which measures the heat of an area of the body, and sweat tests, which can check for the increased sweating seen in the disease.
X-rays can look for bone demineralization and sympathetic blocks can be done to see if this improves the symptoms. Electrodiagnostics, such as an EMG or electromyogram can measure the nerve’s ability to send and receive signals as well as the muscle’s ability to be stimulated by a nerve.
Thermography is somewhat of a reliable tool for making the diagnosis of CRPS. People with this disease have an altered blood flow which changes the temperature of their skin. Other factors that can also alter the blood flow to the patient such as smoking, using certain skin lotions, vasomotor instability, and recent physical activity. Thermographic testing is just one test used to diagnose RSD and related disorders.
Patients can have a powder placed on their extremities that changes color in the presence of sweat. While it is good as a qualitative test for sweat, it doesn’t quantify the amount of sweat. There are two quantitative tests, including the resting sweat output test and the quantitative sudomotor axon reflex test. Such tests are good tests for RSD.
Radiography (x-rays) will show patchy osteoporosis, typical of bones after injury. It can be seen as early as two weeks following the onset of RSD. Doctors can also use bone densitometry to see the changes in bone mineral density. Osteoporosis is very common in RSD.
An EMG (electromyography) and nerve conduction studies can help diagnose RSD and causalgia. They can help differentiate between type I disease and type II disease and can aid in differentiating CRPS from other diseases. CRPS is known as a diagnosis of exclusion – the absence of another disease means that it must be CRPS, such as RSD and causalgia. For example, severe carpal tunnel syndrome can mimic causalgia. The first is treatable easily, while the second is difficult to treat. The EMG and nerve conduction study involve painful testing. There are mild electric shocks involved as well as the insertion of small needles into the skin. Patients experiencing allodynia might not want to undergo these tests that will seem extremely painful.
This involves a three phase radionuclide imaging study on the bone in the area of the pain. It shows diffuse increased uptake and increased perfusion of the affected area, sometimes extending to the shoulder or hip. This increase in activity means there is increased blood flow to the area affected by the disease.
International Association for the Study of Pain (IASP)
The diagnosis from the IASP of complex regional pain syndrome type I (RSD) is as follows:
- Some kind of noxious event that initiates the symptoms (or a prolonged immobilization).
- Ongoing pain and/or allodynia.
- The exaggerated sense of pain out of proportion to the event.
- The presence of edema of the extremity along with changes in blood flow of the skin.
- Abnormal activity of the muscles near the area of pain.
- The absence of any other possible cause of the disease.
For type II CRPS or causalgia, the diagnosis is as follows:
- Ongoing pain, allodynia or elevated sensation of pain following an injury to a nerve, even if it isn’t necessarily in the distribution of the affected nerve.
- Edema, at least some of the time, changes in blood flow of the skin or abnormal activity in the area of the injury.
- The absence of any other cause for the symptoms.