Mast cells in nerve pain

Mast cells are heavily involved in the generation and sensation of pain. The role of mast cells in neurogenic pain (also called nerve pain or neuropathy) is well established and is responsible for a number of painful conditions.

Pain is transmitted like this:

  1. You first feel the pain in nerve endings called nociceptors.
  2. These nerve endings and capillaries in the nearby tissue form a “pain unit” that sends pain signals.
  3. Mast cells are often found close to these nerve endings and capillaries. They release mediators like prostaglandins, histamine and bradykinin.
  4. Nociceptors release mediators like substance P, VIP and CRH, which activate mast cells.
  5. Mast cells then release mediators that increase permeability of the vessels and sensitize the nociceptors. This cycle, in which the nerve endings activate mast cells and the mast cells activate the nerve endings, is called a positive feed back loop. The end result is neurogenic inflammation, or inflammation caused by nerves.

Mast cells can communicate with nerve endings in a number of ways. The first way is by releasing mediators, which may bind to receptors on the nerve cells. A second way is by mast cells sticking to nerve cells through molecules like CADM-1 and N-cadherin; they are able to send signals when their membranes are touching. A third way is by the nerve cells ingesting mediators released by mast cells. These mediators are then transported to other nerve cells, where it can affect which genes are turned on and used.

Mast cells also draw other immune cells to the site of inflammation, like neutrophils and T cells. These cells also release mediators that increase pain, forming another positive feedback loop. The result is that inflammation can spread beyond the initial site of pain, causing a secondary, larger pain response. Hyperalgesia is an exaggerated pain response that is more severe than expected based upon the injury. Mast cells are thought to be directly involved in hyperalgesia and histamine is thought to cause this heightened pain sensation.

Chronic pain has been associated with mast cell degranulation. Degranulation close to colonic nerves is correlated with abdominal pain in IBS patients. Tryptase and histamine can also activate enteric nerves, causing the nerves to be oversensitive. Esophageal pain is also a function of mast cell degranulation.

The specific mechanism of bladder pain due to interstitial cystitis is not clear. However, mast cells are often elevated in IC patients, and contribute to inflammation. It is thought that activation of bladder nerves causes release of substance P by local nerve endings, which activates mast cells.

Overly sensitive and painful skin is sometimes a function of mast cells as well. A significant increase in mast cells has been found in the dermis of fibromyalgia patients. Chronic granulomatous inflammation of the skin causing pain has also been found to be from degranulation of mast cells.

 

References:

Heron, Anne, Dubayle, David. 2013. A focus on mast cells and pain. Journal of Neuroimmunology 264 (2013) 1–7.

Parada, C.A., Tambeli, C.H., Cunha, F.Q., Ferreira, S.H., 2001. The major role of peripheral release of histamine and 5-hydroxytryptamine in formalin-induced nociception. Neuroscience 102, 937–944.

Theoharides, T.C., Kempuraj, D., Sant, G.R., 2001. Mast cell involvement in interstitial cystitis: a review of human and experimental evidence. Urology 57, 47–55.

Theoharides, T.C., Donelan, J., Kandere-Grzybowska, K., Konstantinidou, A., 2005. The role of mast cells in migraine pathophysiology. Brain Res. Brain Res. Rev. 49, 65–76.

Gao, G., Ouyang, A., Kaufman, M.P., Yu, S., 2011. ERK1/2 signaling pathway in mast cell activation-induced sensitization of esophageal nodose C-fiber neurons. Dis. Esophagus 24, 194–203.

The impossible things

I don’t remember the first time I was amazed at what my body could do, but a few episodes come immediately to mind. In 2007, my friend and I got lost while hiking in Norway near Bergen. We lost the moderate grade trail and instead found ourselves very carefully descending rock faces and hiking for several hours longer than expected. We had adequate food and water, decent weather and the benefit of a very late sunset, but almost twelve hours of physical exertion made for a long day.

When we got back to the hostel, it took almost an hour in a hot shower to get all the dirt off. We were exhausted. I crawled into bed and slept deeply, a narcotic, dreamless rest. Just before I fell asleep, I thought to myself that I couldn’t believe that I hadn’t injured myself.

In 2009, I fell through the floor of my attic, which was the ceiling of my front porch. I grabbed a beam as I fell and pulled myself up without hesitation. As I sat on the beam, remembering the image of my legs in the hole with my porch below, I was pretty impressed that I had managed to catch myself. I hit a different beam as I fell and had lots of bumps and bruises, including a huge one right at the top of my leg. In the bathroom mirror, it looked like a black smile.  I was otherwise fine.

There are other moments. The first time I did crow pose. The day I ran a 5K. The several 3-day walks in which I walked sixty miles in three days. Actual feats of physical prowess.

I can no longer do things like that. Maybe I will again someday, but right now, it would be impossible. Still, there are moments when my body amazes me.

I walked down to the harbor yesterday. After weeks of suffocating greyness, 35°F felt like spring. The world outside was thawing, liquid, burning bright with reflected light. I didn’t care how much pain I would be in tomorrow. I just wanted to be alive in a world that was finally thawing, even for a short time.

Boston Harbor was frozen. There were no waves. The water was motionless. Large white globes of ice hung suspended, a crystalline sheen atop the surface. It was otherworldly, and really very beautiful. By the time I got home, I was in a massive amount of pain from the muscular strain of staying stable on ice and snow. I spent last night in bed on muscle relaxers with my heated blanket gathered against the small of my back.

Today the pain is worse and the world is once again encased in ice. But I am renewed in the knowledge that sometimes, my body is still capable of impossible things. I may never climb a mountain again, but in the brief reprieve from a legendary winter, my body walked to the ocean and saw the world doing impossible things, too.

 

Boston Harbor

 

MCAS: Pain

Pain is an unfortunate fact of life with MCAS. Muscle fatigue and weakness are common complaints, but myositis and rhabdomyolysis are rare. Some patients have elevated creatine kinase and/or aldolase, but have no related symptoms.

Bone pain is frequently reported with MCAS. Osteopenia and osteoporosis are common findings. Focal osteosclerosis is also sometimes found, but less frequently. Joints are often painful, which can lead to diagnoses of osteoarthritis, seronegative rheumatoid arthritis, fibromyalgia and polymyalgia rheumatica. Pain can migrate and is often poorly localized. Patients often feel pain in joints, bones and soft tissues, sometimes inconsistently.

Mast cells have been implicated in several pain disorders. Chronic lower back pain has been hypothesized to be related to mast cell activation for over a decade. Complex regional pain syndrome Type I, formerly known as reflex sympathetic dystrophy (RSD) and reflex neurovascular dystrophy (RND), is the most painful long term condition described. It is marked by neurogenic inflammation (nervous system swelling), sensitization of pain receptors and circulatory problems that cause swelling and color changes. It can affect any part of the body. Mast cells have been linked to the inflammatory response seen in CRPS patients.

Neurons with noradrenaline, serotonin and opioidergic receptors inhibit transmission of pain signals. (This is why taking opiates works for pain – it binds to these opioidergic receptors and suppresses the pain signals.) In the spinal cord, pain signals from the peripheral pathways meet up with the spinal pain signals to send to the brain. Here is where molecules like GABA, opioids made in the body and serotonin control pain transmission.

In chronic pain, serotonin acts to amplify the peripheral pain signals instead of suppress them. Increased serotonin levels and mast cell counts are found in many patients with chronic abdominal pain. About 95% of serotonin in the body is found in the peritoneal cavity, which explains the chronic pain many people feel in this region. Mediators released from colon biopsies in IBS patients were proven to excite the local nerves and activate pain receptors. Serotonin is one of these mediators.

Some antidepressants are known to affect serotonin secretion from mast cells. In particular, tricyclic antidepressants inhibit serotonin release in a dose dependent manner at higher concentrations. Clomipramine was seen to be the most effective, with amitriptyline and doxepin inhibiting release of serotonin and histamine at higher doses. All three were found to affect both uptake and reuptake of serotonin by mast cells and therefore lowering the relative concentration of serotonin in the local environment.

MCAS pain is often difficult to treat with typical pain medications. Antihistamines and cromolyn should be used to manage pain where possible. For bone related pain, bisphosphonates are usually effective. There is some data to suggest hydroxyurea can help manage pain in MCAS patients.

 

References:

Xinning Li, MD; Keith Kenter, MD; Ashley Newman, BS; Stephen O’Brien, MD, MBA. Allergy/ Hypersensitivity Reactions as a Predisposing Factor to Complex Regional Pain Syndrome I in Orthopedic Patients. Orthopedics 2014: Volume 37 · Issue 3: e286-e291

Giovanni Barbara, et al. Mast Cell-Dependent Excitation of Visceral-Nociceptive Sensory Neurons in Irritable Bowel Syndrome. Gastroenterology Volume 132, Issue 1, January 2007, Pages 26–37.

Ferjan, F. Erjavec . Changes in histamine and serotonin secretion from rat peritoneal mast cells caused by antidepressants. Inflammation Research 1996, Volume 45, Issue 3, pp 141-144.

Barbara, V. Stanghellini, R. De Giorgio et al. Activated mast cells in proximity to colonic nerves correlate with abdominal pain in irritable bowel syndrome. Gastroenterology, vol. 126, no. 3, pp. 693–702, 2004.

Barbara, B. Wang, V. Stanghellini et al. Mast cell-dependent excitation of visceral-nociceptive sensory neurons in irritable bowel syndrome. Gastroenterology, vol. 132, no. 1, pp. 26–37, 2007.

Afrin, Lawrence B. Diagnosis, presentation and management of mast cell activation syndrome. 2013. Mast cells.

The memory of pain


“It’s so hard to forget pain, but it’s even harder to remember sweetness.  We have no scar to show for happiness.  We learn so little from peace.”  -Chuck Palahniuk, Diary
I’m a medical scientist.  At a conference a few years ago, one of the doctors was recounting a phenomenon we are all familiar with – the patient who swears that their current illness is the worst they have ever had.  It’s not, though.  “They just forget how bad it is,” he surmised.  They are lucky, these normal people.  They get sick a few times a year, so infrequently that the light of their health overwhelms those dark spots. 
I’m not like that, and I don’t think I ever have been.  I’m very grateful for my good days, but when I look back over the landscape for the last few years, that’s not what stands out.  I remember the happiness and enjoyment of those days, but not the physical feeling.  It’s hard to commit the sensation of “less” or “better” to memory; it is merely a fact I can regurgitate when my doctors ask me.  It evokes nothing in me physically. 
I remember pain more than anything else.  I feel like this says something about me as a person, but it’s true.  I spend a lot of time with my pain, after all; it changes and evolves, but never really leaves.  It started in my hands and feet, arthritis that I feel as soon as I open my eyes.  Then my other joints, stiff and sore with motion, throbbing when still.  My lower back, that feels like a seam along which my body will break when I bend.  My lower abdomen, my entire GI tract that burns and twists.  The throbbing in the long bone of my thigh, the twisting in my chest.  The bright red sunburn of anaphylaxis all over my skin.  I have become skilled at cataloguing it, at knowing what is normal and what is new. 
Whether I like it or not, I have learned a lot from my pain.  It has forced me to prioritize my life, to actively pursue the things I want and to eschew what I don’t.  It has forced me to really want things, or to forget about them.  My pain makes me tired and irritable; it guarantees I only spend time with those people who are deeply important to me.  I never do anything just for the sake of doing it.  And in many ways, that is a blessing.
It used to bother me when people talked about being grateful for their illnesses.  I’m not grateful for my illness.  I would rather not have it.  But I like my life, and I like who I am, and my disease is part of the shaping forces responsible.  I am more empathetic now, more organized.  I expect less of people and am let down less.  I deal with disappointment better.  I accept that I cannot do everything I want to.  I suppose I’m grateful for those things, even if I would rather have come to these realizations by another route. 
Sometimes I’ll have a couple good days in a row and I think to myself, maybe this is when it gets better.  Maybe this is when things start steadily improving.  Maybe this is when my pain subsides and I get back the life I had where I could stay out late and drink alcohol and run a 5K and do yoga every day. 
Realistically, that’s never going to happen.  I will never be healthier than I am now; there is too much damage.  But every once in a while it feels like a possibility, and it doesn’t erase the memory of the pain, but it does soften it, just a little.