Moving Towards a Mechanistic Characterization of Chronic Pain Dan Clauw M.D.

Typical Diagnostic Paradigm of Chronic Pain Patient Pain Cause for pain found (?) Abnormality identified Laboratory and radiographic/-oscopic evaluation

How is Chronic Pain Typically Managed? Acute Pain Model Look for “cause” of pain –X-ray, MRI, or – oscopy Treat with medications –Acetaminophen (Tylenol) –Nonsteroidal drugs (Nuprin, Alleve, Celebrex, etc.) –Narcotics If this doesn’t work, we have a tendency to: –blame (drug-seeking, somatizer, high health care utilizer, difficult patient, psychiatric) –ignore –refer Inject it, or cut it out and fix/replace it

Why Are So Many Patients Left With Chronic Pain? Current paradigms are based on the antiquated notion that chronic pain is a symptom, and merely represents acute pain that has lasted too long Recent research has indicated that chronic pain is a disease Most chronic pain that is “left over” after our current treatments, is not due to damage or inflammation of peripheral tissues, but instead due to: –A disturbance in the way the nervous system is processing pain signals –How the individual behaviorally/cognitively responds to the pain

Current Taxonomy for Chronic Pain Syndromes By “disease” –Autoimmune disorders –Cancer pain –Overuse or “wear-and-tear” Osteoarthritis Low back pain –Miscellaneous endocrine or neurological disorders By location –“Idiopathic” disorders

What’s Causing Chronic Pain? Idiopathic Pain Syndromes e.g. fibromyalgia, headaches, irritable bowel 15 – 20% of population have sx. severe enough to seek medical attention frequently co-exist with inflammatory and mechanical disorders Mechanical or “Wear-and-tear” Disorders e.g. osteoarthritis prevalence very age- dependant Autoimmune and Inflammatory Disorders e.g. rheumatoid arthritis, lupus 2 – 3 % of population

Fallacies about Chronic Pain Most chronic pain is due to damage or inflammation of peripheral structures Stimulus Spinal cord from Robert Bennett, MD A-delta – 1 st sharp C fiber – 2 nd burning, throbbing Willis 1985

Pain in SLE (Lupus) 20 – 25% of patients with SLE and other autoimmune disorders have co-morbid fibromyalgia (Clauw 1995) Frequently there is discordance between patient ratings of disease activity and physician’s ratings (Neville 2000) Little or no correlation between objective measures of disease activity (e.g. SLEDAI) or damage (SLICC/ACR) and pain/function; presence of co-morbid FM is best predictor of pain, function (Gladman 1997)

Pain in Osteoarthritis 10% of individuals with knee pain have normal radiographs (Baltimore Longitudinal Study of Aging - Lethridge-Cejku 1995) 30 – 60% of patients with severe osteoarthritis (K-L stages III, IV) have no pain (BLAS - Hochberg 1989; Tecumseh - Carman 1989; Framingham - Felson 1987) More sophisticated imaging studies are more expensive but not more predictive of pain Psychiatric factors (anxiety, depression) can only explain a small percentage of the variance in pain (Creamer 1999)

Chronic Low Back Pain Generally acknowledged to be the most common and expensive musculoskeletal problem in developed countries Abnormal MRI are common in asymptomatic individuals (52% at least one bulging disc, 27% with disc protrusion, 38% > one level abnl.) (Jensen 1994) 50 – 80% of CLBP judged to be “idiopathic” (Deyo 2001) Psychological factors can only explain a small percentage of the variance in pain and function seen in CLBP

Idiopathic disorders Defined largely by location Tension/migraine headache Temporomandibular joint syndrome Regional musculoskeletal pain (e.g., chronic cervical or lumbar pain, whiplash, tendinitis/ “tendinosis”, myofascial pain syndrome) “ Chronic “sinusitis” “Burning mouth” syndrome Esophageal dysmotility, non- cardiac chest pain, “Syndrome X”, costochondritis Biliary dyskinesia, post- cholecystectomy syndrome Interstitial cystitis, female urethral syndrome, vulvar vestibulitis, vulvodynia Irritable bowel syndrome

What Causes Idiopathic Pain Syndromes? Fibromyalgia as a Model Genes “Stress” Cognitive and behavioral adaptation to acute symptoms

Pain Sensitivity in the General Population We all have a “volume control” setting for how our brain and spinal cord processes pain This is likely set by the genes that we are born with, and modified by the environment that we grow up in and live in The higher the volume control setting, the more pain we will experience The most commonly used drugs to treat pain do little to change this “volume” setting Tenderness % of Population

Using Experimental Pain Testing to Examine Pain Processing Hyperalgesia / allodynia distant from site of pain –FM (Petzke/Clauw/Gracely; Geisser/Casey/Crofford) –IBS (Mayer, Naliboff, Chung; Whitehead) –TMD (Maixner; Kashima) –Tension HA (Langemark) –Low back pain (Giesecke) –Vulvodynia/vulvar vestibulitis (Giesecke/Reed) Potential Mechanisms in FM –Wind-up in FM (Price, Staud) –Absence of DNIC (Kosek; Marchand)

Volume + Brain and Spinal Influences on Pain Processing Substance P Glutamate and EAA Serotonin (5HT 2a, 3a ) Neurotensin Nerve growth factor CCK Descending analgesic pathways –Norepinephrine – serotonin (5HT 1a,b ) –Opioids GABA Cannabanoids Adenosine

Which Endogenous Analgesic System(s) are Attenuated in Fibromyalgia? Opioids Normal or high levels of CSF enkephalins 1 Never been administered in RCT but most feel that opioids are ineffective or marginally effective Noradrenergic/Serotinergic Low levels of biogenic monoamines in CSF in FM 2 Nearly any class of drug that raises both serotonin and norepinephrine has demonstrated efficacy in FM 1.Baraniuk et al. BMC Musculoskelet Disord. 2004;5:48. 2.Russell 2.Russell et al. Arthritis Rheum. 1992;35:

The Genomics of Pain Different strains of animals have different pain sensitivity, and pain sensitivity can be modified in “knock-out” mice (Mogill) In 2002, the first demonstration that a genetic polymorphism in the COMT gene caused differences in pain sensitivity in humans (Zubieta) In 2005, the first study demonstrated that pain-free individuals with this gene who were followed for two years, were at higher risk of developing pain (Diatchenko) In the next 3 – 5 years, we will likely identify 20 – 30 genes that control both stress responsivity and pain sensitivity of an individual, and be able to place this on a “chip” that can be used to determine this profile in an individual This will likely cost approximately as much as a single MRI scan

Diatchenko et al, Pain, 2006

What Causes Idiopathic Pain Syndromes? Fibromyalgia as a Model Genes “Stress” Cognitive and behavioral adaptation to acute symptoms

“Stressors” Capable of Triggering These Illnesses (Supported by Case-Control Studies) Peripheral pain syndromes Infections (eg, parvovirus, EBV, Lyme disease, Q fever; not common URI) Physical trauma (automobile accidents) ? Psychological stress/distress Hormonal alterations (eg, hypothyroidism) Vaccines Certain catastrophic events (some wars, but not natural disasters) Clauw et al. Neuroimmunomodulation. 1997;4: ; McLean et al. Med Hypotheses. 2004;63:

“Stress” Related Syndromes Susceptible Individuals Exposure to “Stressors” Mood Disorder PTSD Idiopathic or central pain/fatigue syndrome

What Causes Idiopathic Pain Syndromes? Fibromyalgia as a Model Genes “Stress” Cognitive and behavioral adaptation to acute symptoms

Drugs or surgery can address Non-drug therapies needed to address Functional Consequences of Symptoms Distress Distress Decreased activity Decreased activity Isolation Isolation Poor sleep Poor sleep Maladaptive illness behaviors Maladaptive illness behaviors Initial Symptoms of Pain Damage or inflammation of tissues Damage or inflammation of tissues Disordered sensory processing Disordered sensory processing

Treatment of Idiopathic/Central Pain Syndromes Education Pharmacological therapy Aerobic exercise Cognitive behavioral therapy (CBT) ? Alternative therapies Not reimbursed Use wrong drugs e.g. NSAIDs / opioids Not reimbursed May be working primarily via placebo effect, but is that so bad?

Change in Pain Over Time in Drug Trial Improvement due to “placebo” Improvement due to drug

How Can We Use This Information To Take Better Care of Chronic Pain Patients Now? Identify patients with “central pain” early and manage them differently Pain not well localized and/or multifocal “Peripheral” factors inadequate to account for pain Diffuse tenderness Accompanying somatic symptoms or syndromes Refractory to standard therapies

Tools for Future “Personalized Medicine” in Chronic Pain Diagnosis Genomics Clinical sensory testing Functional imaging Treatment Better drugs Genomics Web-enabled self- management and feedback programs