Dear electdon -

Your statement is partially correct, as applied to the acute case of CRPS in the upper extremities, and even then the results are not infallible. See, e.g., Diagnosis of post-traumatic complex regional pain syndrome of the hand: current role of sympathetic skin response and three-phase bone scintigraphy, Pankaj A, Kotwal PP, Mittal R, Deepak KK, Bal CS, J Orthop Surg (Hong Kong). 2006 Dec;14(3):284-90, ONLINE TEXT @ http://www.rsds.org/2/library/articl...kaj_Kotwal.pdf

Department of Orthopedics, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India.

Abstract
PURPOSE: To evaluate the role of sympathetic skin response (SSR) and three-phase bone scintigraphy (TPBS) in the diagnosis of complex regional pain syndrome (CRPS).

METHODS: 60 patients with CRPS of the hand were recruited. TPBS was performed using a bolus injection of 20 mCi of Tc-99m methylene diphosphonate in an antecubital vein and blood flow (first phase) image, blood pool (second phase) image, and delayed (third phase) image obtained. Patients were considered to have CRPS when the blood pool and blood flow images showed diffuse asymmetric uptake, or when the delayed image indicated increased asymmetric periarticular uptake. SSR was measured simultaneously in the affected and unaffected hands. Standard surface electromyogram disc electrodes were applied to the palm and dorsum of both hands. Electrical stimuli were applied to the skin at the base of little and ring fingers of the unaffected hand. Patients were considered abnormal when response was absent or the peak-to-peak amplitude was <50% of the contralateral hand in at least 2 readings.

RESULTS: The delayed phase of TPBS tested positive in all; the first and second phases tested positive in 54 (90%) and 56 (93%) of the patients, respectively. Four of the 6 patients with a negative first phase had had symptoms persisting for more than 6 months, and the other 2 for about 3 to 6 months. No patient presenting within 3 months had a negative scan. SSR was absent in 16 (27%) patients and normal in 44 (73%). 11 (79%) of 14 patients who presented more than 6 months after symptom onset displayed an abnormal SSR, while only 10% of those presenting within 3 to 6 months and 11% of those presenting within 3 months had an abnormal SSR. 12 (75%) of the 16 patients with abnormal SSR had associated decreased sweating, compared with 2 (4.5%) of the 44 patients with a normal SSR.

CONCLUSION: TPBS is a very sensitive corroborative test to confirm the clinical suspicion of CRPS during the initial stages, but not in late cases. SSR can be used to document the sympathetic dysfunction in cases having an associated sweating abnormality and may have some diagnostic value in late cases of CRPS, when TPBS is less reliable.

PMID: 17200530 [PubMed - indexed for MEDLINE]

http://www.ncbi.nlm.nih.gov/pubmed/17200530

However, when applied to the lower extremities, an altogether different picture emerges. See, generally, Increased soft-tissue blood flow in patients with reflex sympathetic dystrophy of the lower extremity revealed by power Doppler sonography, Nazarian LN, Schweitzer ME, Mandel S, Rawool NM, Parker L, Fisher AM, Feld RI, Needleman L, AJR Am J Roentgenol. 1998 Nov;171(5):1245-50 at 1248:

Bone scintigraphy is, however, only 60% sensitive for lower extremity reflex sympathetic dystrophy and is more likely to be positive in the later clinical stages. [Emphasis added.]

ONLINE TEXT @ http://www.ajronline.org/cgi/reprint/171/5/1245 and citing, Scintigraphic patterns of the reflex sympathetic dystrophy syndrome of the lower extremities, Intenzo C, Kim S, Millin J, Park C, Clin Nucl Med. 1989 Sep;14(9):657-61:

Division of Nuclear Medicine, Thomas Jefferson University Hospital, Philadelphia, Pennsylvania 19107.

Abstract
Thirty-two patients with clinical signs and symptoms of the reflex sympathetic dystrophy syndrome (RSDS) of the lower extremities underwent Tc-99m MDP bone scintigraphy. Twenty-three patients had abnormal scan findings consistent with RSDS, while the scans of the remaining nine patients were normal. Of the 23 patients with abnormal scans, 19 demonstrated increased periarticular activity on early and delayed images, while 4 patients demonstrated decreased activity in the affected limb.

PMID: 2791420 [PubMed - indexed for MEDLINE]

http://www.ncbi.nlm.nih.gov/pubmed/2791420

I, for one, with bi-lateral lower extremity CRPS was burned by false-negative 3-phase bones studies taken roughly 6 months after the onset of my CRPS. In fact, the only thing approaching a significant "test result" early on in the course of the disease was my subjective reporting of going into an almost 10 day remission following the administration of my second lumbar sympathetic block, which, in contrast to the first attempt a week earlier, was applied bi-laterally.

And speaking of blocks, the key in all of this is early intervention and treatment. In a fresh cash of CRPS it is often possible to knock it out with an aggressive series of sympathetic blocks. And specifically in the the arm or hand, a Stellate Ganglion Block, a procedure in which under fluoroscopy a large amount of a local anesthetic (with or without a supplemental steroid) is injected by a pain specialist or an interventional radiologist at the top of the back, approximately where the cervical and thoracic spines transition; and for children the procedure would almost certainly be done under mild sedation. But there, time is absolutely of the essence. See, Efficacy of Stellate Ganglion Blockade for the Management of Type 1 Complex Regional Pain Syndrome, Ackerman WE, Zhang JM, South Med J. 2006; 99:1084-1088, ONLINE TEXT @ http://www.rsds.org/2/library/articl...lion_block.pdf:

Abstract
INTRODUCTION: The purpose of this study was to examine the efficacy of stellate ganglion blockade (SGB) in patients with complex regional pain syndromes (CRPS I) of their hands.

METHODS: After IRB approval and patient informed consent, 25 subjects, with a clinical diagnosis of CRPS I of one hand as defined by the International Association for the Study of Pain (IASP) criteria, had three SGB's performed at weekly intervals. Laser Doppler fluxmetric hand perfusion studies were performed on the normal and CRPS I hands pre- and post-SGB therapy. No patient was included in this study if they used tobacco products or any medication or substance that could affect sympathetic function. The appropriate parametric and nonparametric data analyses were performed and a p value <0.05 was used to reject the null hypothesis.

RESULTS: Symptom onset of CRPS I until the initiation of SGB therapy ranged between 3 to 34 weeks. Following the SGB series, patient pain relief was as follows: group I, 10/25 (40%) had complete symptom relief; group II, 9/25 (36%) had partial relief and group III, 6/25 (24%) had no relief. The duration of symptoms until SGB therapy was: group I, 4.6 +/- 1.8 weeks, group II, 11.9 +/- 1.6 weeks and group III, 35.8 +/- 27 weeks. Compared with the normal control hand, the skin perfusion in the CRPS I affected hand was greater in group I and decreased in groups II and III.

DISCUSSION: The results of our study demonstrate that an inverse relationship exists between hand perfusion and the duration of symptoms of CRPS I. On the other hand, a positive correlation exists between SGB efficacy and how soon SGB therapy is initiated. A duration of symptoms greater than 16 weeks before the initial SGB and/or a decrease in skin perfusion of 22% between the normal and affected hands adversely affects the efficacy of SGB therapy. [Emphasis added.]

PMID: 17100029 [PubMed - indexed for MEDLINE]

http://www.ncbi.nlm.nih.gov/pubmed/17100029

See, also, Complex regional pain syndrome type I: efficacy of stellate ganglion blockade, Istemi Yucel, Yavuz Demiraran, Kutay Ozturan, Erdem Degirmenci, J Orthopaed Traumatol (2009) 10:179–183, ONLINE TEXT @ http://www.ncbi.nlm.nih.gov/pmc/arti...Article_71.pdf

And the truth of the matter is that no single test can substitute for the clinitian's judgment. See, The incidence of complex regional pain syndrome: A population-based study, de Mos M, de Brijn AGJ, Huygen FJPM, Dieleman JP, Stricker BHC, Sturkenboom MCJM, Pain 2007;129:12-30, at 20:

Limitations in our study are related to the absence of a gold standard for the diagnosis of CRPS. As observed in the specialist letters, physicians focused on vaso- and sudomotor and motor-trophic signs, whereas the presence or absence of sensory and neurological symptoms was not frequently reported.

ONLINE TEXT @ http://www.rsds.org/2/library/articl..._pain_2006.pdf

And indeed, it is only the prompt exercise of informed judgment by an experienced clinitian that can make seeming magic like this possible: A Unique Presentation of Complex Regional Pain Syndrome Type I Treated with a Continuous Sciatic Peripheral Nerve Block and Parenteral Ketamine Infusion: A Case Report, Everett A, Mclean B, Plunkett A, Buckenmaier C, Pain Medicine 2009 Sep;10(6):1136-9. Epub 2009 Sep 9, ONLINE TEXT @ http://www.rsds.org/2/library/articl...n_Plunkett.pdf

Mike