• Changes in somatosensory phenotype at one year assessed with Quantitative Sensory Testing (QST)
• Motor function of the affected extremity at one year assessed with a biometric evaluation
• Changes in Health Related Quality of Life at one year assessed with SF-36
• Changes in plasma endocannabinoid levels at 30, 60, 90 days and at one year

The purpose of this study is to determine whether application of low dose Delta9-Tetrahydrocannabinol can prevent the development of chronic pain in patients with acute CRPS.

Recent animal data suggest that the endocannabinoid system is a promising target in the prevention of chronic pain. It has been shown that the endocannabinoid system modifies excitatory and inhibitory currents in structures involved in the development of chronic pain such as the amygdala.

CRPS is a neuropathic pain condition, which is known to become chronic in a significant percentage. The study compares the effect of low dose Delta9-Tetrahydrocannabinol (90 days) and placebo in acute CRPS. All patients will receive a standard treatment consisting of drug therapy and physiotherapy.

• Complex Regional Pain Syndromes
• CRPS

• Rolke R, Baron R, Maier C, Tolle TR, Treede RD, Beyer A, Binder A, Birbaumer N, Birklein F, Botefur IC, Braune S, Flor H, Huge V, Klug R, Landwehrmeyer GB, Magerl W, Maihofner C, Rolko C, Schaub C, Scherens A, Sprenger T, Valet M, Wasserka B. Quantitative sensory testing in the German Research Network on Neuropathic Pain (DFNS): standardized protocol and reference values. Pain. 2006 Aug;123(3):231-43. Epub 2006 May 11.
• Azad SC, Monory K, Marsicano G, Cravatt BF, Lutz B, Zieglgansberger W, Rammes G. Circuitry for associative plasticity in the amygdala involves endocannabinoid signaling. J Neurosci. 2004 Nov 3;24(44):9953-61.
• Azad SC, Eder M, Marsicano G, Lutz B, Zieglgansberger W, Rammes G. Activation of the cannabinoid receptor type 1 decreases glutamatergic and GABAergic synaptic transmission in the lateral amygdala of the mouse. Learn Mem. 2003 Mar-Apr;10(2):116-28.

Inclusion Criteria:

• Patients with clinical diagnosis of acute CRPS (time from inciting event less than 16 weeks) of the upper extremity
• No risk of dependency in a psychological assessment

Exclusion Criteria:

• History of alcohol or drug abuse
• Cardiac arrhythmias
• Acute or chronic renal failure
• ASA physical status classification III or higher
• Psychiatric disorders
• Pregnancy and breast feeding

• German Federal Ministry of Education and Research
• German Research Network on Neuropathic Pain