Complex Regional Pain Syndrome Type 1 (Reflex Sympathetic Dystrophy) Imaging
Updated: Mar 15, 2023
Author: Lawrence E Holder, MD; Chief Editor: Felix S Chew, MD, MBA, MEd
Practice Essentials
Complex regional pain syndrome type 1 (CRPS 1), formerly known as reflex sympathetic dystrophy (RSD), is an incompletely understood response of the body to an external stimulus, resulting in pain that is usually nonanatomic and disproportionate to the inciting event or expected healing response. Current taxonomy categorizes CRPS 1 as occurring in the absence of definable nerve injury. In many cases, CRPS follows a relatively minor trauma, usually a sprain, twist, dislocation, or soft tissue injury. In some cases, no previous injury was recalled. In children, fractures are the precipitating event in about 5-14% of cases and surgical procedures in about 10-15%. Type II, which was previously caused causalgia, occurs in the presence of nerve trauma. CRPS affects daily function, sleep, and activities of daily living and can have a significant effect on mental and psychosocial well-being. [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
CRPS 1 is diagnosed on the basis of clinical manifestations, and there are limited laboratory tests or image studies to verify the diagnosis. The International Association for the Study of Pain (IASP) has developed criteria (also known as the Budapest criteria) for the clinical diagnosis of complex regional pain syndrome.[9] Several diagnostic procedures, such as bone scintigraphy, plain radiographs, quantitative sensory testing, skin temperature measurements, and fMRI are used to support the diagnosis of CRPS.
Currently, there are no specific pathologic, histologic, or biochemical markers for CRPS 1.[11, 12, 13, 14, 15, 16] However, there is increasing evidence to show that inflammatory processes and immune reactions are involved in the pathophysiology of CRPS.[17] In a systemic review and meta-analysis, Parkitny et al concluded that CRPS is associated with proinflammatory states in the blood, blister fluids, and cerebrospinal fluid. The CRPS-related inflammation may change the sympathetic tone of blood vessels and, therefore, affect blood supply and tissue oxygenation. The acute and chronic phases of CRPS demonstrate different inflammatory features in both clinical manifestations and inflammatory profiles.[18]
(The radionuclide bone scans below depict patients with CRPS 1.)
Reflex sympathetic dystrophy of the hand. Delayed image palmar view reveals increased tracer diffusely involving the entire right wrist, metacarpals, and phalanges, with juxta-articular accentuation. Relatively less increased uptake is observed distally, but all areas are involved. The dot of increased activity distal to the third ray is a hot marker indicating the right side.
Reflex sympathetic dystrophy of the foot. Delayed image plantar view reveals increased tracer uptake diffusely involving the lowermost right leg, ankle, tarsals, metatarsals, and phalanges. Uptake is less distally than proximally, but all areas are involved. The dot of increased activity distal to fifth toe is a hot marker indicating the right side.
Radiologic examination
Radionuclide bone imaging (RNBI) is the only generally accepted imaging technique to provide objective and relatively specific evidence of CRPS 1 in the upper and lower extremities, predominantly the hands and feet.[19, 20, 21, 22, 23] Delayed bone imaging has been reported to be up to 100% sensitive for the variant of sympathetically maintained pain termed RSD by hand and foot surgeons.[24, 25]
Plain radiography is only 60% sensitive and is not specific; when radiographs are positive, they often show only osteoporosis, occasionally in combination with soft tissue swelling or diffuse soft tissue atrophy. Plain radiographs of the affected limb can rule out any localized pathology to the bones, joints, and surrounding tissue.[8] Although osteoporosis is found in as many as 60% of patients with upper extremity reflex sympathetic dystrophy (RSD), it is not specific, often representing changes of disuse secondary to the pain associated with CRPS 1. Occasionally, soft tissue swelling or diffuse soft tissue atrophy may be seen; these are nonspecific findings. No consistent findings have been found in the occasional study done with other imaging modalities, and none are suggested for diagnosis.
Magnetic resonance imaging (MRI) changes in established CRPS 1 have rarely been evaluated, and as with studies using other modalities, the definition of CRPS has varied considerably. In one study by Schweitzer et al involving the lower extremity (N=35), soft tissue thickening with and without contrast enhancement (N=31) was demonstrated without any marrow changes,[26] while in another study of the upper extremity (N=17), by Koch et al,[27] no marrow changes and only inconsistent soft tissue or muscle signal changes were seen.
Magnetic Resonance Imaging
Ultrasonography
Although ultrasound is not an established technique in the imaging evaluation of CRPS 1, musculoskeletal ultrasonography can identify myofascial structural lesions and may help distinguish neuropathic pain from CRPS. In a retrospective observational study, musculoskeletal ultrasonography results of 7 patients with neuropathic pain were compared to those of 7 patients with CRPS 1. Muscles in patients with CRPS 1 were characterized by a variable and/or global intramuscular structural disruption with loss of muscle bulk. Adjacent muscles coalesced with one another to present a uniform hyperechogenic mass of tissue. Muscle edema was present in some patients. In comparison, muscles affected by neuropathic pain exhibited structural normalcy but also showed considerable reduction in muscle bulk.[28]
Nuclear Imaging
Three-phase radionuclide bone imaging (RNBI) is performed primarily because the differential diagnosis often includes infection or other lesions for which information about the perfusion to the extremity (phase I) or relative vascularity of the extremity (phase II) is helpful.[29, 30, 31, 32]
For CRPS 1 of the hand or foot, the hallmark on the radionuclide angiogram (RNA; phase I) is diffuse increased perfusion to the entire extremity, including the distal forearm or leg and, occasionally, reaching the shoulder or hip, even when the inciting lesion is distal.
Similar diffuse increased vascularity, manifested by diffuse increased tracer accumulation on blood pool or tissue-phase images (phase II) is seen. On these images, juxta-articular accentuation may be seen. RNA findings are abnormal in approximately 40% of patients and blood pool findings in approximately 50%, most often in clinical stage I or II of the disease.
Delayed images demonstrate diffuse increased tracer throughout the hand or foot, including the wrist or ankle, with juxta-articular accentuation and, often, proximal uptake involving the forearm or leg and, occasionally, the shoulder and arm or hip and femur. Activity in the hands or feet usually is more prominent proximally than distally, but the amount of abnormal tracer uptake has not been correlated with clinical severity. Quantification occasionally has been helpful but is not used routinely.
(See the images below.)
Reflex sympathetic dystrophy of the hand. Delayed image palmar view reveals increased tracer diffusely involving the entire right wrist, metacarpals, and phalanges, with juxta-articular accentuation. Relatively less increased uptake is observed distally, but all areas are involved. The dot of increased activity distal to the third ray is a hot marker indicating the right side.
Reflex sympathetic dystrophy of the foot. Delayed image plantar view reveals increased tracer uptake diffusely involving the lowermost right leg, ankle, tarsals, metatarsals, and phalanges. Uptake is less distally than proximally, but all areas are involved. The dot of increased activity distal to fifth toe is a hot marker indicating the right side.
Pediatricians report a moderate frequency of lower extremity neurovascular or neuroregulatory disease in children that has been termed reflex sympathetic dystrophy. In these children, a bone scan pattern often reveals marked decreased tracer uptake on delayed images compared to increased uptake in adults; therefore, this may represent a different condition, such as pseudodystrophy.
When radionuclide bone imaging (RNBI), especially in the upper extremity, demonstrates classic diffuse findings, RSD is certain. When RNBI does not demonstrate that pattern, the most common variant of sympathetically maintained pain syndrome (SMPS) or CRPS 1 is excluded.
In the lower extremity, patients with severe infection, especially if underlying diabetes mellitus is present, may demonstrate diffuse increased delayed image tracer uptake on RNBI performed to diagnose osteomyelitis. This is not usually a diagnostic issue clinically.
Intervention
CT-assisted temporary thoracic sympathetic nerve blockade
According to Andresen et al, outpatient CT-assisted temporary thoracic sympathetic nerve blockade is an effective adjunct therapy, with a low complication rate, for complex regional pain syndrome (CRPS). In their study, in addition to physiotherapy and pharmacotherapy with analgesics and calcitonin, sympathetic nerve blockade was performed 3 times, at 2-day intervals. The CT-assisted puncture was performed in the prone position at the level of the intervertebral space of the second and third thoracic vertebrae. All patients reported immediate pain relief. Color-coded duplex ultrasonography of the arteries of the affected limb was performed before and after puncture and showed increased peripheral blood flow.[33]
Kastler reported using CT-guided radiofrequency neurolysis for treating patients with refractory type I CRPS of the upper limb.[34] Inclusion criteria were clinically based using the International Association for the Study of Pain (IASP) criteria plus a positive stellate ganglion block.[35]
Ultrasound-guided pulsed radiofrequency
A patient who developed CRPS following injury to the saphenous nerve achieved sustained pain relief after the administration of ultrasound-guided pulsed radiofrequency for the management of intractable pain of the lower limb.[36]
Photoacoustic Microscopy
It has been suggested that measurement of microcirculatory parameters, such as blood flow rate, blood volume, and oxygen saturation (sO2) with photoacoustic microscopy (PAM) might be used to potentially diagnose the presence of CRPS, to indicate the activity of the disease, and to monitor the effectiveness of the therapeutic intervention. In a prospective observational study of 8 adult patients with CRPS 1 and pain in one upper extremity undergoing stellate ganglian block (SGB), peripheral blood vessels in 2 sites in patients’ hands were imaged by PAM systems. From pre- to post-SGB block, a 50% increase occurred in signal intensity of PAM and a 4% increase occurred in sO2, which agreed with the increased temperature and decreased pain level. The results showed that blood perfusion increased after SBG, which is consistent with prior reports.[37]