**7. Reflex sympathetic dystrophy**

Reflex sympathetic dystrophy (RSD) is a complex physiologic response of the body to an external stimulus resulting in pain sympathetically mediated, usually nonanatomic pattern, which is out of proportion to the inciting event or expected healing response (Fournier & Holder 1998). It is a syndrome affecting an extremity after a minor trauma or surgery, but the particular mechanism remains uncertain. The diagnosis of RSD relies on clinical evaluation, scintigraphy or MR imaging, and routine radiographs. In the spontaneous course of this syndrome three phases can be distinguished: Stage I is the warm or hypertrophic phase, stage II is called the cold or atrophic phase and the third stage corresponds to stabilization or, in rare instances, to healing (Driessens et al., 1999; Ornetti & Maillefert, 2004).

Fig. 4. Bone scanning: Diffusely increased uptake in the distal right upper extremity in reflex sympathetic dystrophy.

Three-phase scintigraphy has been widely utilized in both the diagnosis and monitoring of treatment (Murray, 1998). Scintigraphy imaging (**Fig. 4**) shows increased perfusion during the angiographic and vascular pool phases and widespread increases in radiophosphonate bone uptake in the late stage (Colamussi et al., 2004). The highest diagnostic accuracy is provided by the combination of three signs: Increase activity ratio in the blood pool phase performed at 5-15 min, diffuse uptake in the carpus o tarsus and periarticular uptake in all the small joints (Murray, 1998). Decreased radiotracer accumulation has also been described, especially in children and adolescents (Driessens et al., 1999; Love et al., 2003). Bone scintigraphy is of major importance for the diagnosis in order to clearly differentiate from other conditions which are incorrectly diagnosed and treated as RSD. If the bone scan is not suggestive of RSD, the clinical picture, radiological examination and vascular scan may lead to the correct diagnosis. This may be a pseudodystrophy, in which a hypovascularization is found right from the start, while in true RSD there is initially a hypervascularization. Other conditions which may be confused with RSD are causalgia, neurotic compulsive postures, hysterical conversion, malingering and even self-mutilation (Driessens et al., 1999). Bone scintigraphy has a high sensitivity in the initial stage of Sudeck's syndrome, but after 26 weeks, it loses accuracy (Benning & Steinert, 1988; Lee & Weeks, 1995).
