Intraarticular Application of Opioids Versus Glucocorticosteroids Versus Placebo in Rheumatoid Arthritis

Study background

Patients with chronic inflammatory arthritis (e.g. rheumatoid arthritis, undifferentiated oligoarthritis, monarthritis) suffer from recurrent pain, functional impairment and impaired capacity. Consequences of such hard to treat diseases are occupational incapacity and early retirement. The treatment options we have today such as nonsteroidal antirheumatic drugs (NSAIDs such as diclofenac), glucocorticosteroids (e.g. dexamethasone) and disease modifying antirheumatic drugs (such as methotrexate) partly are effective but also have serious side effects and complications (e.g. gastric and duodenal ulcers, nephrotoxicity, degeneration of cartilage, cushing´s syndrome...).

A new therapeutic approach without such complications is represented by the intraarticular (i.a.) application of low-concentrated, systemically inactive dosages of an opioid (e.g. morphine). This treatment showed a significant reduction of pain in patients with chronic arthritis in controlled clinical trials without systemic or local side effects [1, 2]. This effect is based on an activation of peripheral opioid receptors, which could be identified on peripheral nerve endings of sensoric neurons [3-5]. The activation of these opioid receptors leads to a decrease of neuronal excitability and the transmission of noziceptive impulses as well as to a reduced release of proinflammatory neurotransmitters (e.g. substance p) [6]. Several studies showed that locally applied opioids act analgetic, that such analgetic effects mainly occur in inflamed tissue, that the analgetic effects increase with the degree of inflammation and that peripherally acting opioids act analgetic [6-9]. In human beings the analgetic effect of peripherally applied opioid agonists has almost only been shown in patients with acute post-surgical pain [4, 10-15]. In a first case report [16] we found indices for the analgetic effect of i.a. given morphine in patients with chronic arthritic pain. In patients with osteoarthritis a double blind cross-over study it was shown that 1mg morphine leads to a long-lasting analgetic effect up to 9 days [1]. In a second controlled trial we compared patients with chronic joint inflammation in different diseases in regards of the analgetic effect of i.a. morphine (3 mg) versus placebo versus a standard therapy with i.a. dexamethasone (4 mg) [2]. Dexamethasone as well as morphine lead to a significant pain reduction under rest and under strain compared to placebo. This analgetic effect lasted up to 6 days after injection. Moreover we found first indications for an anti-inflammatory effect as the number of inflammatory cells in the synovial fluid was reduced after the i.a. morphine application [2].

In addition to the question whether morphine can stimulate local peripheral opioid receptors, it should be investigated, whether intraarticular morphine has an anti-inflammatory local effect in arthritis of the knee in the setting of inflammatory rheumatic diseases such as rheumatoid arthritis, spondyloarthropathies, undifferentiated oligoarthritis or monarthritis (17, 19, 31). This question should be answered through investigation of cellular infiltration and cytokine expression in the synovial membrane and synovial fluid.

Next to the exogenous application of opioids also endogenous opioid peptides play an important role in inflammatory processes. Experimental and clinical investigations show an expression of opioid peptides in immune cells, which invade into inflamed tissue [3, 4, 6, 20, 21]. Under certain circumstances these opioid peptides are locally released and unfold a strong analgetic effect through the activation of opioid receptors on peripheral sensoric nerve endings [22-24]. Corticotropin-releasing factor (CRF) can release - similar as in the hypophysis- opioid peptides from immune cells [25-28]. CRF receptors are located in regionally invaded immune cells, and the number is up regulated among inflammatory cells. [29]. Experimental investigations from our or other groups showed a significant analgetic effect of local CRF which was given into the inflamed tissue [24, 26, 30].