Complex regional pain syndrome (CRPS) is a rare, chronic pain disorder. CRPS is challenging for patients and physicians because it leads to significant morbidity due to chronic pain that can last years. CRPS typically develops four to six weeks after direct trauma, such as an injury (e.g., fracture) or surgery.¹ Many treatment recommendations for CRPS are based on smaller studies or consensus guidelines and on practice. Although most cases of CRPS resolve spontaneously without treatment,² the pain, associated symptoms, psychological impact, and disability require a well-informed, patient-centered approach.

Epidemiology

CRPS is three or four times more common in women than in men, and the peak age of onset is between 50 and 70 years.^2–4 Few studies have looked closely at the incidence of the disease, and most data are from retrospective reviews of medical databases. These reviews estimate that the incidence of CRPS is five to 26 per 100,000 people per year.² Because diagnostic criteria have been revised over time across multiple specialties, the reported incidence may be underestimated.^1,3 Research has shown that among patients with fracture, the incidence of CRPS is anywhere from 0.05% to 0.2% in older studies and 3% to 7% in more recent studies, although the diagnostic criteria varied.⁵

Because of the variety of symptoms and fluctuation of symptom severity over time, symptoms of CRPS may be attributed to malingering or somatization. However, no psychological or personality traits have been shown to predispose an individual to CRPS.⁶ Although comorbid Axis I disorders, especially major depression, are present in up to 49% of patients with CRPS, there is no evidence that comorbid psychiatric disorders are more common in those with CRPS compared with other patients who have chronic pain.⁷

Pathophysiology

CRPS has been subdivided into reflex sympathetic dystrophy (type 1) or causalgia (type 2). Type 1 CRPS accounts for 90% of cases and begins after an injury with no nerve involvement on nerve conduction testing. Confirmation of nerve injury on nerve conduction testing is the defining feature of type 2 CRPS.⁷ Both types are treated similarly.

The pathogenesis of CRPS is poorly understood, and although many causal mechanisms have been postulated, it is likely multifactorial. It is unclear why most cases of CRPS develop after an injury, but some do not. Possible causal mechanisms include combinations of local inflammatory cascades, direct small fiber nerve injury, dysfunction of the sympathetic nervous system, central pain processing, and emotional responses to painful stimuli.^8,9 Some studies also suggest that an autoimmune process plays a role in CRPS.^10,11 Genetic factors may be involved, but strong associations have not been identified.¹²

Clinical Presentation

Initial symptoms of CRPS include pain out of proportion to the inciting injury that is usually described by patients as burning, tingling, stabbing, numbness, or an electric shock¹ and is localized to a distal extremity (CRPS rarely develops in other parts of the body). Other symptoms at the site of pain include increased growth of hair or nails (trophic changes), increased sweating, localized swelling, and hyperemia.³ Of CRPS cases, 40% develop after a fracture.⁵

Symptoms typically begin within four to six weeks after the inciting incident, and the pain can last years. Pain associated with CRPS does not correspond to a dermatomal or nerve root distribution and usually is not associated with a specific nerve injury (type 1 CRPS). Many patients with CRPS are unable to use the affected extremity because movement can worsen the pain. The signs and symptoms of CRPS can vary widely between patients and within a disease course.¹³ Table 1 includes the documented frequency of signs and symptoms in patients with CRPS.^3,8,14,15