Introduction

Overview of polymyositis

“Poly” means many, the root word “myo” is muscle; and “itis” means inflammation. So the word polymyositis means inflammation of many muscles. Polymyositis is a rare connective tissue disorder that causes inflammation of muscles, tendons, and ligaments. As a result, muscles become swollen, tender, painful, start to break, and progressively become weaker, impairing the quality of life of the patient and even causing disability or death in some cases.¹ Polymyositis belongs to a larger group of crippling diseases called inflammatory myopathies, others include dermatomyositis and inclusion body myositis. In an individual with polymyositis and dermatomyositis, skin-related manifestations occur along with muscular inflammation.²

Introduction to dermatologic manifestations associated with dermatomyositis

Dermatomyositis is a form of polymyositis with cutaneous symptoms. Skin manifestations may include skin rashes, swelling around the eyes and at the base and sides of fingernails, and splitting of the skin of the fingers.²

Background and pathophysiology

Causes and risk factors of polymyositis

DM (dermatomyositis) affects both children and adults, while PM (polymyositis) is more common in middle age from 45-60 years of age. Both diseases are more common in female gender with 2:1.² 

A few risk factors associated with both disorders are as follows:³

Genetics

The major histocompatibility complex (MHC) has a strong genetic association with polymyositis and other myopathies, though specific genes that contribute to pathogenesis are still unclear.

Environmental factors

Several environmental factors have been shown to trigger autoimmune responses in the body, causing disease flare-ups. Infections like urinary tract infections (UTI), gastroenteritis, coxsackie B virus, HIV, and chronic hepatitis B virus (HBV) are associated with developing PM and DM. Sun exposure, UV radiation, and NSAIDs are significant contributors to DM. Other factors include chemicals, gut microbiota, pollutants, cancer, and smoking.

Presence of other autoimmune diseases 

This includes diseases like lupus, rheumatoid arthritis, scleroderma, or Sjögren’s syndrome.

Mechanisms underlying the development of dermatologic manifestations

PM and DM are autoimmune disorders where the body's immune cells become abnormally activated to harm the body's tissues. However, the types of immune cells responsible and target tissues differ in both. In PM, CD8+ T cells surround and target MHC 1 expressing muscle fibres, causing them to die. In DM, CD4+ T-cells attack vascular endothelium causing perivascular inflammation, capillary necrosis (death), and muscle fiber destruction. Interferon and cytokines secreted by activated T cells are found in the skin and muscles of patients with DM and PM.³ Dermatomyositis is microangiopathy, and dermatologic manifestations are the result of vasculopathy, Koebner’s phenomenon or photosensitivity usually.^3,6

Clinical presentation

Common symptoms of polymyositis are:

• Difficulty climbing stairs, rising from a sitting position, and raising arms above shoulders
• Difficulty lifting the head if neck muscles are involved
• Difficulty swallowing and speaking due to weakness of throat muscles and oesophagus
• Fever
• Joint pain
• Lethargy

Common skin manifestations observed in dermatomyositis 

• Heliotrope rash: Blue-purple discolouration on upper eyelids associated with oedema⁴
• V sign: Erythematous rash on face, neck and chest
• Gottron’s sign: Reddish macules or patches on the outer surface of elbows and knees
• Shawl sign: Rash on the back of shoulders
• Nail fold bleeding
• Skin ulcer
• Mechanics hand: Rough, cracked hyperkeratotic lines on lateral and palmer surfaces of fingers
• Gottron’s papules (hallmark sign): Red to violet-coloured papules or plaques on the outer surface of finger joints

Diagnostic approaches

Diagnostic criteria and methods for polymyositis

The Bohan and Peter’s criteria is a widely accepted diagnostic criteria for both polymyositis and dermatomyositis.^3,5

Bohan and Peter’s criteria

Laboratory tests that are used to confirm the diagnosis of polymyositis and dermatomyositis are: 

• Serum muscle enzymes (like LDH, aspartate and creatine kinase, of which creatine kinase is most sensitive⁸
• Electromyography
• Muscle biopsy (gold standard)
• Muscle MRI
• Skin biopsy (in some cases of dermatomyositis)
• Myositis autoantibodies 

Limitations in diagnosing dermatomyositis

The first step towards an effective treatment strategy is an early, correct diagnosis of a disease. However, because dermatomyositis is a systemic autoimmune disease, its widespread multisystem involvement and overlapping symptoms with polymyositis make it challenging to diagnose. 

Also, there is a lack of clear diagnostic criteria, such as the limitations of Bohan and Peter’s criteria, which cannot distinguish polymyositis and dermatomyositis from inclusion body myositis and other myopathies. This is because when these criteria were proposed in 1975, tests for myositis-specific autoantibodies were not available, hence, a combination of lab tests is required along with a proper history and a detailed examination, as most patients may not have a typical presentation and signs and symptoms can vary widely from person to person. Muscle weakness associated with a cutaneous manifestation should raise suspicion for dermatomyositis immediately.

Treatment and management

Pharmacological interventions and the importance of a multidisciplinary approach

The primary goal of treatment for polymyositis and dermatomyositis is to improve the quality of life of the patient by increasing muscular strength and to help with the self-esteem of dermatomyositis patients by managing their skin concerns. Hence, if treatment improves serum creatine kinase (CK) levels but is unable to show physical improvement, that therapy cannot be considered effective. This defines the important role of a multidisciplinary approach in dealing with both dermatomyositis and polymyositis. 

Treatment options for dermatologic manifestations and muscle weakness 

Immunosuppressive agents are the mainstay of treatment. A few are discussed below:^3,7

Glucocorticoids

They are the first-line therapy with an oral prednisone dosage of 1 mg/kg of body weight. Dexamethasone has shown fewer side effects as compared to prednisone.

Immunomodulators

Immunomodulators such as azathioprine, methotrexate, cyclosporine, and mycophenolate are considered second-line for treating severe, rapidly progressing, or refractory cases.

Biological agents

Biological agents like rituximab and TNF inhibitors are also used for refractory or unresponsive diseases.

Non-pharmacological treatment options include physical therapy, exercise, diet, and lifestyle modifications. Exercise is effective in improving aerobic capacity and muscle strength. Creatine supplements, alongside exercise, also showed great improvement in patients in a clinical trial. 

Patients who are on steroids are advised to consume a low-fat, low-carb, and low-salt diet to reduce side effects of medication such as weight gain, hypertension, diabetes, and oedema. Calcium and vitamin D supplements are recommended to minimise the risk of osteopenia. Speech therapy is helpful for individuals who have throat muscle weakness.³

Prognosis and complications

Long-term outcomes and complications

Both PM and DM are chronic illnesses that have lifelong symptoms. As the disease progresses, it shows more systemic organ involvement and results in mild to severe disability in later stages of life.

Complications of polymyositis include:

• Dysphagia leading to weight loss and malnutrition
• Aspiration pneumonia
• Respiratory failure
• Congestive heart failure
• Myocarditis
• Arrhythmias

Factors influencing prognosis and management decisions

According to a study held in the United States, the 10-year survival rate of PM/DM patients is 62%. Death is mainly caused by cardiopulmonary complications (22%), infections (15%), and cancer (11%).²

Factors influencing the prognosis of polymyositis and dermatomyositis include:

• Gender
• Age at the time of diagnosis
• Presence of Raynaud’s phenomenon
• Interstitial lung disease
• Respiratory involvement
• Cardiac involvement
• Dysphagia
• Juvenile dermatomyositis
• Calcinosis in dermatomyositis

FAQs

How can dermatomyositis and polymyositis be prevented?

There is no known preventive method for this condition yet. Most of the data from controlled clinical trials is limited to determining if any specific gene or factor can be controlled to prevent these diseases. 

What is the cure for dermatomyositis and polymyositis?

There’s no cure for these diseases and they are lifelong illnesses. The treatment is only symptomatic and can help suppress the immune system when there is a flareup. However, an early diagnosis and a holistic approach to the condition can greatly help with symptom management and prevent severe complications. 

What is the best way to manage the symptoms of polymyositis and dermatomyositis? 

To best manage the symptoms of PM and DM, individuals should consider the following steps:

• Talk to your healthcare provider as soon as you start to experience muscle weakness, any skin rash, or both, and do not delay the treatment, especially if it persists for 6 months or more
• Follow the doctor’s advice religiously, and be consistent with medication or any exercises suggested by the physical therapist or speech therapist, as medication alone is not as effective for rebuilding the damaged muscles as when combined with physical therapy
• Avoid UV exposure by limiting sun exposure, refraining from tanning beds, and wearing broad spectrum SPF of at least 50 during the day and reapplying it every 2 hours
• Schedule regular follow-ups with your doctor to monitor your symptoms and labs

How long will it take for symptoms to improve once treatment is started?

This can vary individually as treatment efficiency depends on various factors like type of treatment, severity of symptoms, age of onset of disease, with old age showing a poor prognosis, and time interval from disease onset to the start of treatment.

Summary 

Polymyositis and dermatomyositis are two well-known inflammatory myopathies with a low incidence rate of 1 in 100,000, hence, basic clinical research to understand pathogenesis, progression, diagnosis, and safe treatment procedures remains inadequate. As a result, misdiagnosis and delayed treatment are two great challenges faced by health experts and patients.