Neuromuscular Disorders 101: The Break Down of Polymyositis

Foreword

Neuromuscular disorders cause major changes in an individual's daily function and independence. Its broad term encompasses a large variety of diseases with different presentations. As healthcare evolves, so does clinical research updating disease diagnostic criteria and treatment options for neuromuscular disorders. This series will discuss neuromuscular disorders from a health science point of view concerning the etiology, pathophysiology, and treatment of neuromuscular disorders. The series will also discuss in depth the types of disorders and their etiology, diagnosis criteria, and medical rehabilitation management.

The series is divided into the following eight chapters:

1. Neuromuscular Disorders 101: Living with Peripheral Neuropathy

2. Neuromuscular Disorders 101: The Progression of Muscular Dystrophy

3. Neuromuscular Disorders 101: The Effects of Amyotrophic Lateral Sclerosis

4. Neuromuscular Disorders 101: The Break Down of Polymyositis

5. Neuromuscular Disorders 101: Charcot-Marie-Tooth Disease: Effects on Childhood to Adulthood

6. Neuromuscular Disorders 101: The Dysfunction of Multiple Sclerosis

7. Neuromuscular Disorders 101: In the Face of Myasthenia Gravis

8. Neuromuscular Disorders 101: Infection to Impairment: Guillain-Barre Syndrome

Neuromuscular Disorders 101: The Break Down of Polymyositis

Polymyositis is a progressive, autoimmune inflammatory disease that attacks skeletal muscle causing inflammation and severe weakness (“Polymyositis”, 2022; “Polymyositis”, n.d.). It is known to cause weakness on both sides of the body in a symmetrical pattern. General onset of polymyositis is more common in adults than children. Final stages of the disease severely debilitate an individual's ability to function normally and thus their independence, as patients begin to have difficulty swallowing, talking, reaching overhead for personal hygiene activities and rising from sit to stand positions (“Polymyositis”, n.d.). Patients with progressive polymyositis may also develop additional impairments such as shortness of breath, irregular heartbeat, and heart failure. Currently, there is no cure for polymyositis, treatment is focused on preserving muscular strength and function. In this article we will discuss the etiology, diagnostics, and medical management associated with polymyositis.

Etiology/Pathophysiology

Polymyositis is an autoimmune disorder whose etiology is due to abnormal activation in immune system cells where they began to attack muscle tissue, causing a condition called rhabdomyolysis (“Polymyositis”; n.d.; Sarwar, 2022). Rhabdomyolysis is defined as the breakdown of damaged muscle which releases proteins and electrolytes into the bloodstream (“Rhabdomyolysis”, 2023). The release of these muscle cell contents can cause organ damage as well as permanent disability, or mortality. While the exact cause is unknown, researchers have proposed the pathological processes of the disease are related to abnormal activation of cytotoxic T cells, or CD8 T cells (immune cells that kill other cells such as foreign and infected cells) (“Cytotoxic T Cell”, n.d.; Sarwar, 2022). This abnormal activation causes a cellular immune response which mistakenly reads as an attack from a viral or foreign substance in the musculature. This altered immune response results in these T cells injuring healthy muscular tissue. This CD8 T cell infiltration in polymyositis is located in the endomysium (connective tissue that surrounds each muscle fiber (Bosques & Singh, 2022; “Epimysium”, n.d.). In healthy muscular tissue, the plasma membrane of a muscle cell (sarcolemma) does not activate molecules called major histocompatibility complex (MHC) class I (Bosques & Singh, 2022; “Major histocompatibility complex”; 2023; Sarcolemma, n.d.). MCH class I assists in helping the immune system recognize foreign substances in the body, and are located in nearly all cell membranes in humans. However, in polymyositis it is suspected that MCH class I causes an altered activation of CD8 T cells which bind to MCH class I and release cell damaging proteins and cause muscle cell death.

Figure 1. Layers of skeletal muscle (Miller, 2020)

Disease Overview

Polymyositis has been shown to be more common in women and usually affects adults over the age of 20 years, with a reported incidence of 3.8 per 100,000 persons in the United States (Holloman & Mohila, 2021; Sarwar et al., 2022). Disease reports reveal that the disease is more common in Black Americans than in White Americans (Bosques & Singh, 2022). Polymyositis in children (juvenile polymyositis) is uncommon as these cases only make up 4% of the disease patient population. The common age range for polymyositis to occur in adults is 40 to 60 years old with an estimated five-year survival rate to be more than 80% and a ten-year survival rate of 90% (Bosques & Singh, 2022; Holloman & Mohila, 2021). Older adults suffering from cardiovascular disease and difficulty swallowing report having higher mortality rates associated with polymyositis. Risk of developing the disease is increased if a person also suffers from other autoimmune diseases such as lupus, rheumatoid arthritis, and Sjogren’s syndrome (“Polymyositis”, 2022).

Symptom onset is usually seen as gradual and progressive muscle weakness that is symmetric and in proximal (closer to one’s torso) than distal (i.e. legs and arms) areas. (Bosques & Singh, 2022). Patients also report symptoms of morning stiffness, fatigue, fever and weight loss, usually over a period of 3 to 6 months. Most patients state the weakness is painless, with a minority of cases (less than 30%) reporting pain. The pelvic area has been shown to be more involved than in the upper body, so patients may complain of difficulty transitioning from a sitting to standing position (Sarwar, 2022). Patients with upper body weakness may complain of difficulty with activities of daily living (i.e. hair washing/combing), inability to raise arms, or holding their neck fully upright. Other complaints other than weakness include frequent falls, difficulty swallowing, shortness of breath, and constipation. On physical examination, patients may complain of soreness with touch along with decreased muscle strength and reflexes.. (Bosques & Singh, 2022; Sarwar, 2022). Muscle atrophy, or muscle wasting is not visible unless the patient’s condition is chronic and muscle reflexes are unremarkable, however in severe weakness or chronic stages reflexes may be entirely absent. In severe cases, abnormal lung sounds may be evident with respiratory examination which indicate interstitial lung disease (ILD), a broad term used for a group of lung disorders that cause lung tissue inflammation and/or damage (Hadjiliadis, 2021).

Figure 2. Overview of myositis, including polymyositis (Miller, n.d.)

Diagnosis

Diagnostic testing for polymyositis includes imaging and laboratory testing. Mayo Clinic (2022) describes the diagnostics utilized for polymyositis as follows:

Blood tests. A blood test will let your doctor know if you have elevated levels of muscle enzymes, which can indicate muscle damage. A blood test can also detect specific autoantibodies associated with different symptoms of polymyositis, which can help in determining the best medication and treatment.

Electromyography. This test involves inserting a thin needle electrode through the skin into the muscle. Electrical activity is measured as you relax or tighten the muscle, and changes in the pattern of electrical activity can confirm a muscle disease. The doctor can determine the distribution of the disease by testing different muscles.

Magnetic resonance imaging (MRI). A scanner creates cross-sectional images of your muscles from data generated by a powerful magnetic field and radio waves. Unlike a muscle biopsy, an MRI can assess inflammation over a large area of muscle.

Muscle biopsy. During this test, a small piece of muscle tissue is surgically removed for laboratory analysis. Analysis may reveal abnormalities, such as inflammation, damage, certain proteins or enzyme deficiencies.

Polymyositis Case Report

A case report conducted by Tan et al. (2021) investigated a 56 year-old female diagnosed with polymyositis initially with cardiac symptoms. The patient’s complaint was chest pain occurring intermittently. The reported pain was increasingly aggravated for a timespan of one hour during a shoulder massage the patient had received. The patient stated she did not take any medication for the pain episode. Providers conducted cardiac testing, such as an electrocardiogram (measures electrical activity of the heart) which indicated abnormalities in heart rhythm. The patient was initially diagnosed with myopericarditis (inflammation in heart tissues, specifically the pericardium and myocardium). During the patient’s hospital admission, she experienced a new onset of a fever and irregular heart beat. However, despite receiving proper treatment for myopericarditis, the patient continued to experience fever which was accompanied with weakness and fatigue. The patient tested negative for infection. Further testing was conducted by providers which showed increased creatine kinase levels and magnetic resonance imaging (MRI) testing revealed degraded musculature proximally. The patient’s muscle biopsy revealed T cell infiltration, confirming a polymyositis diagnosis as well. The authors clarified the patient’s diagnosis of polymyositis with cardiac involvement of myopericarditis.

Figure 3. Overview of diagnostic testing for myositis, including polymyositis. (Miller, n.d.)

Medical Management

Rehabilitation services such as physical, occupational, and speech therapy assist patients with polymyositis to maintain functional and preserve as much functional muscular strength as they can, such as strengthening how to safely swallow by learning exercises and compensation strategies (“Polymyositis”, 2022). However, in later stages of the disease, swallowing tends to get worse and patients may benefit from a dietetic assessment by a dietitian to prepare foods that are easier to consume with progressive stages of polymyositis. Pharmacological approaches for disease treatment include oral corticosteroids which are considered the “first line” of treatment (Holloman & Mohila, 2021; Sarwar et al., 2022). Corticosteroids are beneficial in controlling symptoms of the disease, however prolonged use of these medications can cause serious side effects therefore providers usually taper down doses over time (“Polymyositis”, 2022). One corticosteroid used is Prednisone, which assists in the control of inflammation that is caused during an immune response in polymyositis. Prednisone is used to restore some muscular strength in patients to improve essential functioning such as swallowing, breathing, and cardiovascular functions (“Polymyositis (PM)”, n.d.). Due to the side effects that occur with prolonged use, providers prescribe a corticosteroid-sparing medication that is used in combination with corticosteroids to decrease the dose and side effects of corticosteroids. The second option of treatment in patients that do not respond or experience adverse effects to steroids is the use of medications termed “immune-modulators” to suppress the overactive immune system that occurs with polymyositis (“Immunomodulating agent”; n.d.; Sarwar et al., 2022). In chronic cases of polymyositis, intravenous immunoglobulins (IVIG) may be utilized (Sarwar et al., 2022) where there is a reported improvement in condition around 70% in patients and significant improvement in muscle power after short-term IVIG use (Cherin et al., 2022). IVIG is a therapy treatment where health antibodies are injected into a patient from health donors (Ursani, 2022). These healthy antibodies interfere with a patient’s own antibodies and their immune system’s reaction to overactivation of CD8 T cells (“Polymyositis (PM)”, n.d.).

Conclusion

Polymyositis is a progressive autoimmune disease where an altered immune response in the body begins to attack muscle tissue, causing severe weakness in skeletal muscles (“Polymyositis”, n.d.). Progressive courses in the disease can cause irregular heart rhythms, shortness of breath, ILD, and difficulty with speech. Diagnostics for polymyositis include a patient’s complaints of body weakness on both sides of the body and present in more proximal areas of the body (i.e. pelvic area, shoulders, neck), with usual reports of non painful weakness. Other diagnostic testing used are blood tests, muscle biopsy and electromyography to confirm polymyositis. Medical management is tailored to moderating a patient’s immune system with corticosteroids to decrease damage to muscle cells from T cell attacks; therapy services are also heavily utilized in polymyositis to improve muscle strength and function. Further research is needed for exact etiology and curable methods for the disease.

Bibliographical References

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