Myositis: Symptoms, Types, Causes and Treatment

Myositis is a rare, complex group of disorders characterized by inflammation of the skeletal muscles. While the main feature is muscle weakness, myositis can affect multiple organs, presenting a range of symptoms and challenges for patients and clinicians alike. With several subtypes, various causes, and evolving treatment strategies, understanding myositis is essential for timely diagnosis and effective management. This article provides a comprehensive, evidence-based overview of the symptoms, types, causes, and treatments for myositis.

Symptoms of Myositis

Recognizing myositis starts with understanding its symptoms. The impact can be subtle or severe, often affecting daily life and well-being. Early recognition is crucial for effective intervention.

Symptom	Description	Frequency/Pattern	Source(s)
Muscle Weakness	Progressive, often proximal muscles	Symmetrical or asymmetrical	1 3 4 5 7
Muscle Pain	Aching, soreness, tenderness	Variable, not always prominent	2 3 4
Fatigue	Persistent tiredness	Systemic	4 7
Dysphagia	Difficulty swallowing	Common in some types	3 5 7
Skin Rash	Red/purple rash, notably on face/hands	Especially in DM/JDM	4 5 7
Extramuscular	Lung, joint, heart, GI involvement	Subtype-specific	5 6 7

Table 1: Key Symptoms

Major Muscular Manifestations

Muscle weakness is the hallmark of myositis. In most subtypes—such as polymyositis (PM), dermatomyositis (DM), and immune-mediated necrotizing myopathy (IMNM)—the weakness is symmetrical and mainly affects the muscles closest to the trunk (proximal muscles), such as the hips, thighs, shoulders, and upper arms. This leads to difficulties in climbing stairs, rising from a chair, or lifting objects overhead 3 4 5 7.

Inclusion body myositis (IBM), on the other hand, often presents with asymmetrical weakness, more commonly affecting distal muscles (such as those in the wrists and lower legs), sometimes with muscle atrophy 3 4 5 7.

Muscle pain—while possible—is less common and, when predominant, may suggest other diagnoses 3 4. Fatigue and a general sense of malaise are frequently reported.

Extramuscular Symptoms

Myositis can extend beyond the muscles:

• Dysphagia (difficulty swallowing) is common, especially when the muscles of the upper esophagus are involved. Persistent dysphagia may result from muscle fibrosis 3 5 7.
• Skin symptoms are classic in dermatomyositis and juvenile dermatomyositis, with rashes appearing on the face, knuckles, and elbows 4 5 7.
• Other organ involvement includes:
  • Lungs: Interstitial lung disease, especially in overlap and antisynthetase syndromes
  • Joints: Arthritis or arthralgia
  • Heart and gastrointestinal tract: Rare, but possible 5 6 7

Recognizing Disease Variability

Symptoms can vary in severity and pattern, sometimes mimicking other neuromuscular or systemic diseases. This variability underscores the importance of careful clinical evaluation and use of diagnostic tools like MRI, electromyography (EMG), and muscle biopsy 1 3 7.

Types of Myositis

Myositis is not a single disease, but a family of related disorders, each with unique features, age of onset, and prognosis.

Type	Key Features	Typical Age/Pattern	Source(s)
Dermatomyositis (DM)	Muscle weakness, distinctive skin rash	Children & adults	1 4 5 6 7 8
Polymyositis (PM)	Proximal muscle weakness, no rash	Adults	1 4 5 6 7
Inclusion Body Myositis (IBM)	Distal > proximal weakness, slow progression	Older adults	1 3 4 5 6 8
Immune-mediated Necrotizing Myopathy (IMNM/NAM)	Severe weakness, high CK, rapid onset	Adults	1 5 7 8 12
Overlap Myositis/Antisynthetase Syndrome (OM/ASS)	Myositis + features of other autoimmune diseases	Adults	1 5 6 7 8
Juvenile Dermatomyositis (JDM)	DM in children, prominent skin and muscle symptoms	Children	4 12

Table 2: Main Types of Myositis

Dermatomyositis (DM) & Juvenile Dermatomyositis (JDM)

DM is characterized by proximal muscle weakness and a unique skin rash, often on the face, eyelids, knuckles, and elbows. JDM is the childhood form, with similar features but sometimes a more acute or severe course 4 5 6 7 12. Both can present with extramuscular manifestations, such as lung involvement.

Polymyositis (PM)

PM typically affects adults and presents as progressive, symmetrical proximal muscle weakness without a skin rash. It can be challenging to distinguish from other subtypes and is now considered less common due to refined diagnostic criteria 1 4 5 6 7.

Inclusion Body Myositis (IBM)

IBM is unique for its slow, progressive muscle weakness, which is often more pronounced in distal muscles (e.g., wrist/finger flexors, quadriceps). It affects older adults, is usually asymmetric, and is notoriously resistant to treatment 1 3 4 5 6 8.

Immune-Mediated Necrotizing Myopathy (IMNM/NAM)

IMNM features severe muscle weakness with marked elevation of muscle enzymes (CK), and a rapid onset. It is often associated with specific autoantibodies (e.g., anti-SRP, anti-HMGCR) and can be triggered by statins or, rarely, infections 1 5 7 8 12.

Overlap Myositis & Antisynthetase Syndrome (OM/ASS)

These forms are defined by the coexistence of myositis with features of other connective tissue diseases (such as scleroderma or lupus), or by the presence of specific autoantibodies (e.g., anti-Jo-1). Lung involvement is particularly common and can dominate the clinical picture 1 5 6 7 8.

Causes of Myositis

Understanding the root causes of myositis is critical for both prevention and management. Research highlights a complex interplay between genetics, immune dysfunction, environmental triggers, and sometimes infections.

Cause Type	Examples/Mechanisms	Notes/Associations	Source(s)
Autoimmunity	Aberrant immune response, autoantibodies	Most common in IIMs	4 5 6 7 9
Genetic Factors	HLA variants, genetic susceptibility	Modifies risk	9 10
Environmental	Viruses, bacteria, UV light, drugs, toxins	Triggers in susceptible individuals	4 10 12
Infections	Bacterial, viral, fungal, parasitic myositis	Infectious myositis	2 4 10 12
Cancer	Paraneoplastic, especially in DM/NAM	Cancer-associated	11 12
Drugs	Statins, biologics, certain supplements	Drug-induced myopathy	4 10 12

Table 3: Main Causes and Risk Factors

Autoimmune Mechanisms

Most inflammatory myopathies are autoimmune in nature. The body’s immune system mistakenly targets muscle tissue, causing inflammation and damage. Discovery of myositis-specific autoantibodies (MSAs) has revolutionized diagnosis and helps define subtypes and prognosis 4 5 6 7 9.

Genetic and Environmental Factors

Genetic predisposition, especially involving certain HLA types, increases risk. However, genetics alone are insufficient—environmental triggers such as viral or bacterial infections, ultraviolet radiation, smoking, occupational exposures, and certain drugs (notably statins) play a role in initiating disease in susceptible individuals 4 9 10 12.

Infectious Myositis

While most myositis cases are autoimmune, infections can directly cause muscle inflammation. Bacteria (e.g., Staphylococcus aureus), viruses (e.g., influenza, HIV), fungi, and parasites can infect muscle, leading to localized or generalized myositis 2 4 10 12. Infective myositis often presents more acutely and is managed differently than autoimmune forms.

Cancer Association

Some myositis cases, especially dermatomyositis and necrotizing autoimmune myopathy, are linked to underlying cancer (paraneoplastic syndromes). Certain autoantibodies (e.g., anti-TIF1γ, anti-NXP2, anti-HMGCR) are associated with a higher risk of malignancy, suggesting cancer may trigger immune-mediated muscle injury 11 12.

Drug-Induced Myositis

Certain medications, particularly statins, can trigger immune-mediated necrotizing myopathy. Other drugs, including biologics and dietary supplements, have also been implicated 4 10 12.

Treatment of Myositis

Effective management of myositis requires a tailored, multidisciplinary approach. While treatment advances are ongoing, early intervention can significantly improve outcomes.

Treatment	Purpose/Use	Notes/Outcomes	Source(s)
Glucocorticoids	First-line, reduce inflammation	High-dose, then taper	13 16 17
Immunosuppressants	Steroid-sparing, for maintenance	MTX, AZA, MMF, etc.	13 16 17
Biologics	Refractory or specific subtypes	Rituximab, others	13 16 17
IVIG/SCIG	Severe/refractory cases	Rapid effect, safe	14 16 17
Exercise	Improve strength/function	Safe, improves outcomes	13 15 16
Supportive Care	Physical/occupational therapy	Multidisciplinary needed	13 15
Cancer Therapy	For paraneoplastic myositis	Treat underlying cancer	11 17

Table 4: Main Treatment Options

Pharmacologic Therapy

Glucocorticoids

High-dose corticosteroids are the mainstay initial treatment for most inflammatory myopathies, aiming to quickly control muscle inflammation. Once symptoms and muscle enzymes improve, the dose is gradually tapered to minimize side effects 13 16 17.

Immunosuppressive Agents

Commonly used as steroid-sparing agents or for maintenance therapy, these include methotrexate (MTX), azathioprine (AZA), and mycophenolate mofetil (MMF). Choice depends on disease severity, subtype, and patient factors 13 16 17.

Biologics

Biologic agents such as rituximab (anti-CD20) may be considered in refractory cases or when certain autoantibodies are present. Other biologics are under investigation in clinical trials 13 16 17.

Immunoglobulin Therapy (IVIG/SCIG)

IVIG and subcutaneous immunoglobulin (SCIG) can be effective in severe or treatment-resistant cases, particularly for rapidly progressive disease, severe dysphagia, or in juvenile dermatomyositis. These therapies can improve muscle strength and have a steroid-sparing effect 14 16 17.

Non-Pharmacologic Management

Exercise and Rehabilitation

Supervised exercise programs (aerobic and resistance training) are safe and strongly recommended for all patients, including those with active disease. Exercise reduces impairment, improves quality of life, and may even decrease disease activity 13 15 16.

Multidisciplinary Support

Management often requires a team approach, including physical therapists, occupational therapists, speech-language pathologists (for dysphagia), and sometimes pulmonologists, cardiologists, or oncologists, depending on organ involvement 13 15.

Special Considerations

• IBM: Unlike other types, IBM is largely resistant to immunosuppressive therapy, and management focuses on supportive care and rehabilitation 1 4 5.
• Paraneoplastic Myositis: Treating the underlying malignancy is essential, in addition to standard immunosuppressive therapy 11 17.
• Monitoring & Relapse: Regular monitoring of muscle strength, enzyme levels, and extramuscular symptoms is important, as relapses can occur, particularly during steroid tapering 14 16 17.

Conclusion

Myositis encompasses a spectrum of rare, complex muscle diseases with significant variability in symptoms, causes, and outcomes. Key points include:

• Symptoms: Muscle weakness is the central feature, but myositis can affect multiple organs, with fatigue, dysphagia, and skin rashes as common signs.
• Types: Main forms include dermatomyositis, polymyositis, inclusion body myositis, immune-mediated necrotizing myopathy, overlap/antisynthetase syndromes, and juvenile forms.
• Causes: Autoimmune mechanisms predominate, influenced by genetics and environmental triggers (infections, drugs, cancer).
• Treatment: Early, aggressive immunosuppression (glucocorticoids plus immunosuppressants), IVIG, and supervised exercise form the therapeutic backbone, supported by a multidisciplinary team.

Staying informed about myositis enables patients and clinicians to recognize symptoms early, pursue appropriate diagnostic testing, and engage in effective, individualized management. Ongoing research promises further advances in treatment and improved outcomes for those affected by this challenging group of diseases.