Why It Hurts. Dr. Aneesh Singla

      Chapter 1

       What is Pain?

      Think of pain as a speech your body is delivering about a subject of vital importance to you.

      —Paul Brand, The Gift of Pain: Why We Hurt & What We Can Do About It

      One Sunday afternoon while cleaning out my garage, I noticed some bottles of beer that needed to be moved to the refrigerator. I picked them up and, as I turned to open the fridge door, one slipped out of the carton and smashed on the concrete floor behind me. The pressurized liquid sounded like an explosion. Shards of glass lay scattered across the garage floor. When I knelt down to sweep them up, I noticed a twinge in my left leg. Upon examining my calf, I discovered a two-inch-long gash, but I hadn’t felt anything at the time of the injury. The explosive sound had startled me so much, it had completely distracted me from the experience of the injury.

      Physical pain is a universal experience. (There are certain people who do not feel pain, as we will discuss in Chapter 2, but they are extraordinarily rare exceptions.) While the sensation is unpleasant—at best—it serves a vital function by teaching us how to adapt to our surroundings.

      For example, when we are young, we learn that we experience pain when we touch something sharp. Thus, we learn to avoid sharp objects to avoid further damaging our bodies. Pain, in short, is an adaptive and protective sensation.

      Types of Physical Pain

      The body uses physical pain to get our attention when something is amiss. Someone’s jaw hurts; the dentist discovers an infected tooth and pulls it. Someone’s abdomen hurts; the family doctor diagnoses appendicitis and orders an emergency appendectomy. These pains are acute. Acute pain develops immediately after an injury or another distinct event. By contrast, chronic pain develops over time and generally lasts for months or longer.

      Acute and chronic physical pain can be further classified as inflammatory, nociceptive, or pathological. Rheumatoid arthritis and osteoarthritis are two familiar kinds of inflammatory pain. Inflammation occurs when our immune system responds to an injury by sending an army of infection-fighting cells to destroy invaders in our bodies. This response results in warmth, swelling, and hypersensitivity, along with pain. In the case of an autoimmune disease like rheumatoid arthritis, the body mounts an immune response to harmless tissue that is misinterpreted as dangerous. This results in infection-fighting cells, which produce antibodies, to attack the cushioning and shock-absorbing cartilage in our joints.

      “Doc,” one patient with arthritis said, “my hip feels like I have a constant toothache.” His pain was chronic and inflammatory.

      Nociceptive pain results from physical trauma such as a skin laceration or a burn from a hot stove. It’s a response by the nervous system to a physical event that damages our body. This is generally a sharp, stabbing, or cutting sensation in the area of the injury, depending on the type of damage inflicted. Acute, nociceptive pain is what I experienced when I bent down to clean the garage floor and discovered the gash on my calf.

      Pathological, sometimes called neuropathic, pain has no adaptive purpose. In fact, it is often referred to as maladaptive pain because it provides no specific protective function. From an evolutionary perspective, it does not confer a survival advantage. Typically, this type of pain is due to nerve injury or nervous system dysfunction. Depending on the type of nerve involved, a patient suffering from pathological pain might feel a burning, stabbing, or electrical sensation with no injury to account for it. As you can imagine, this kind of pain presents unique challenges for diagnosis and management because it is more difficult to identify its underlying cause.

      Unlike neuropathic pain, inflammatory and nociceptive pains are considered to be adaptive. Think of a smoke detector. Working properly, it sounds an alarm whenever there is enough smoke in the air to indicate a fire. Thus, it serves a vital adaptive function: alerting you to evacuate before your house burns down. Adaptive pain is the body’s smoke detector. It signals an alarm—a pain sensation—whenever pain receptors are triggered by damage to your cells. It’s the body’s way of saying, “Take your hand off that stove before the burn gets any worse.” That is a classic example of nociceptive pain.

      When you do get a burn, on your finger for instance, the pain you feel for days afterward is inflammatory. This is the pain from the inflammation response at the site of the healing tissue. The body’s smoke alarm is still serving its purpose by alerting you that the cells are busy healing injured tissue. Even though it’s annoying, the inflammatory pain is there for a very good reason: to tell you that your finger is not ready for the next task at hand. Achy, tired joints and muscles while fighting off the flu are another example of adaptive inflammatory pain. In this case, the pain suggests you rest and let the body fight off the virus.

      Of course, smoke detectors aren’t always right. Sometimes, they go off when there’s a bit of smoke but no danger of a house fire. For example, I recently overdid it searing some salmon for dinner. Off goes the ear-piercing smoke alarm, and up the ladder I go to wave the smoke away. In the body, this kind of false alarm is known as pathological pain and, unfortunately, waving a towel around it isn’t going to help.

      Pathological pain is a kind of hurt that occurs when an acute injury hasn’t occurred, a maladaptive pain. For example, people with trigeminal neuralgia, also known as tic douloureux, experience severe jaw pain. There is nothing physically wrong with the jaw, but the pain alarm sounds loudly and ceaselessly, without serving any adaptive or protective purpose.

      When someone presents with any type of physical pain, one of the first steps in evaluating the problem is to ask a series of diagnostic questions: Where does it hurt? Does it radiate? Would you describe it as sharp or dull? Shooting? Can you give a number to your pain, with zero being no pain and ten being the worst pain imaginable?

      Doctors may order a barrage of tests: X-rays, MRIs, blood work, and so on. They then try to piece it all together to form a diagnosis. When a cause is detected, the patient is either sent to a specialist (e.g., a urologist to treat a kidney stone) or treated on the spot (e.g., with antibiotics for a urinary tract infection). In cases of pathological pain, however, test results may show nothing abnormal. Such perplexing cases usually require the intervention of a pain specialist like me.

      Beyond inflammatory, nociceptive, and pathological pain, there is the realm of psychological pain. Both physical and psychological pains require a diagnostic workup to get to the underlying cause. There are parallels in the diagnostic processes of a psychologist or psychiatrist: “I see you are anxious and depressed. Can you describe the sensation of your anxiety? Do you know what kinds of situations trigger your depression?”

      Anxiety, with or without pain, can be adaptive. For example, if you’re worried about an upcoming test, your anxiety may push you to study. As you firm up your knowledge of the test material, your anxiety should fade. Anxiety can also be maladaptive. If you suffer from an anxiety disorder like agoraphobia, the irrational fear of open spaces, it can prevent you from even holding a job that requires leaving the house. This would require proper psychiatric treatment