Experimental models of arthritis: Identification of substance P as a therapeutic target and use of capsaicin to manage joint pain and inflammation

Efficacy of topical interventions for temporomandibular disorders compared to placebo or control therapy: a systematic review with meta-analysis

This systematic review focused on the efficacy of topical products in reducing temporomandibular joint disorder (TMD)-associated pain, in comparison to placebo or control interventions. The EMBASE, Web of Science, Cochrane Library, and MEDLINE via PubMed databases were searched for randomized controlled trials (RCTs) using topical interventions in adults diagnosed with TMD. The pain intensity was the primary outcome, and other clinical findings were the secondary outcomes. The risk of bias was evaluated according to the Cochrane's handbook. The search up to February 7, 2020 identified a total of 496 unduplicated references. Nine RCTs with 355 adult patients diagnosed with TMD were included. The meta-analysis did not show a significant reduction in baseline pain intensity in the nonsteroidal anti-inflammatory drug (NSAIDs) group, when compared to the placebo group (P = 0.288). One study demonstrated a statistically significant pain score decrease for Theraflex-TMJ compared to placebo after 10 d of treatment (P = 0.003) and follow-up, 5 d after the last application (P = 0.027). Ping On reduced pain at 4 weeks of application (P < 0.001) but not after 7 d of application (P = 0.136). In one study, cannabidiol (CBD) significantly improved the pain intensity compared to placebo (P < 0.001). However, no differences were found with capsaicin in the two studies (P = 0.465). Evidence was of low quality because the studies were considered as having an unclear or a high risk of bias and a small number of studies were analyzed. The evidence is not sufficient to support the use of topical NSAIDs and capsaicin, and limited evidence was found for Threraflex-TMJ, bee venom, Ping On, and CBD, with only one study reporting for each. Additional studies are recommended to validate these results.

Intra-articular Botulinum Toxin Type A: a new approach to treat arthritis joint pain

There is a growing need for novel treatments of refractory arthritis joint pain as the aging population is expanding with many patients who are unable to undergo joint replacement surgery. We are studying the efficacy and safety of intra-articular injection of Botulinum Toxin Type A (IA-BoNT/A) into joints with arthritis pain. In several small open label studies, initial effects for IA-BoNT/A were encouraging because two thirds of the patients had more than 50% reduction in joint pain severity that was associated with a significant improvement in function. Importantly no serious adverse effects of IA-BoN/A were noted. Based on these initial results, we have completed two pilot randomized controlled trials in painful shoulder joints and painful knee joints. In the shoulder study, IA-BoNT/A produced a significant decrease in shoulder pain severity at one month (6.8-4.4 on VAS, p=.002) that was also significantly better than the non-significant change after IA-Saline placebo (1.6 unit difference favoring IA-BoNT/A, p=.014). In the knee study IA-BoNT/A produced a significant 48% decrease in McGill Total Pain Score at one month (p=.01 1) that was still significant at 3 mo after injection (p=.002). There was a strong placebo response in one third of those but the decrease in pain severity was not significant. We are currently conducting a RCT of IA-BoNT/A for painful prosthetic knee joints. Based on these initial studies of IA-BoNT/A we have gone 'back to the bench' to standardize a menu of pain behaviors for mice with acute inflammatory arthritis pain and chronic inflammatory arthritis pain. IA-BoNT/A significantly reduced arthritis joint tenderness (evoked pain score) in acute and chronic inflammatory arthritis and normalized impaired spontaneous wheel running in mice with chronic inflammatory arthritis but not in those with acute inflammatory arthritis. With these models of arthritis and pain behavior methods we will be able to screen potential intra-articular analgesics, define dose response curves and injection schedule, and study the relationships of articular pain and loss of function.

Topical agents in the treatment of rheumatic disorders

Topical drug delivery may be the optimal route for the treatment of localized musculoskeletal disorders because higher drug concentrations can be achieved at the sites of clinical significance. The rationale for the use of topical salicylates and other nonsteroidal anti-inflammatory drugs (NSAIDs) in the treatment of soft-tissue rheumatic complaints and osteoarthritis is reviewed. Topical capsaicin offers another potentially beneficial therapy for the treatment of osteoarthritis of selected joints. Although there are extensive, uncontrolled experiences with DMSO that suggests its effectiveness in the treatment of musculoskeletal disorders, controlled trials yield conflicting results. The basis for the use of physical modalities such as phonophoresis and iontophoresis to improve topical drug efficacy is summarized.

Non-NSAID pharmacologic treatment options for the management of chronic pain

Chronic pain affects 75 million US citizens. A number of pharmacologic treatments are available for chronic pain that does not respond adequately to nonpharmacologic methods. Long the mainstay of chronic pain management, nonsteroidal anti-inflammatory drugs (NSAIDs) are known to be associated with gastrointestinal (GI) and renal toxicities, a particular problem for the elderly population, which commonly experiences chronic pain, such as that associated with osteoarthritis (OA). Several non-NSAID, non-narcotic therapies are available for noninflammatory pain. Acetaminophen is as effective as NSAIDs for the management of mild-to-moderate OA pain and is the recommended first-line therapy by the American College of Rheumatology (ACR). Propoxyphene, widely believed to be safe and effective, may, in fact, be no more effective-and perhaps less effective-than acetaminophen or ibuprofen. A relatively new analgesic, tramadol, appears to be a useful therapy for patients who do not receive adequate pain relief with acetaminophen and are at risk for NSAID-related side effects. For localized chronic pain associated with OA, topical capsaicin is also an effective analgesic.

Approach to the management of nonmalignant pain

Pain is a universal, subjective, unpleasant sensation. It results from a noxious stimulus that causes the body to perceive existing or potential damage to its organs. The biochemical mechanism of pain is based on peripheral nociceptors that preferentially receive noxious stimuli and thereafter cause the primary afferent nociceptor fibers to release endogenous chemicals such as bradykinin, histamine, prostaglandins, serotonin, norepinephrine, and substance P. Additionally, substance P may stimulate prostaglandin and collagenase production, thus providing an explanation for the effectiveness of anti-inflammatory drugs in relieving pain. The interpretation of pain is highly individualized and embodies the entire personality. Thus, no two patients with pain can be treated in the same way. Pain is assessed through medical history, physical examination, and a variety of pain scales. General principles in managing pain call for the physician to (1) respect pain; (2) recognize the psychologic components of pain; and (3) treat the underlying disorder in a timely fashion. Modern management of pain evokes a multidisciplinary approach that includes patient education, pharmacologic intervention, physical medicine, minimally invasive procedures, psychologic counseling, behavioral modification and, in some instances, surgery or a variety of other nonpharmacologic modalities.