Idiopathic Inflammatory Myopathies Overview

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Questions and Answers

Which of the following is a characteristic symptom of idiopathic inflammatory myopathies (IIM)?

Loss of sensation in limbs

Extreme fatigue without muscle involvement

Uncontrolled muscle spasms

Severe muscle weakness (correct)

Which of the following conditions can cause secondary muscle involvement similar to idiopathic inflammatory myopathies?

Heart disease

Neuromuscular junction disorders (correct)

Asthma

Vitamin D deficiency (correct)

Which form of myositis is characterized by muscle weakness associated with other connective tissue diseases?

Adult-onset PM

Immune-mediated necrotizing myositis

Juvenile-onset DM

Overlap myositis (correct)

Which of the following infectious agents can lead to myositis?

Borrelia burgdorferi Signup and view all the answers

In a case of idiopathic inflammatory myopathy, what is an expected finding in laboratory tests?

Elevated creatine kinase (CK) levels Signup and view all the answers

Which of the following is NOT classified as an idiopathic inflammatory myopathy?

Duchenne’s muscular dystrophy Signup and view all the answers

What is the typical annual incidence of idiopathic inflammatory myopathies?

2–19 cases/million Signup and view all the answers

Which of the following best represents a juvenile form of idiopathic inflammatory myopathy?

Juvenile-onset DM Signup and view all the answers

Which nutritional disorder can contribute to muscle issues resembling idiopathic inflammatory myopathies?

Vitamin D deficiency Signup and view all the answers

Which of the following endocrine disorders may show significantly elevated CK levels?

Hypothyroidism Signup and view all the answers

What should be assessed to differentiate steroid myopathy from IIM exacerbation?

Creatine kinase (CPK) levels Signup and view all the answers

What characterizes the skin manifestations of amyopathic dermatomyositis (DM)?

Only cutaneous symptoms with no muscle involvement Signup and view all the answers

Which symptom is commonly associated with antisynthetase antibody (ASA) syndrome?

Mechanic’s hand Signup and view all the answers

What feature distinguishes immune-mediated necrotizing myositis (IMNM) from other forms of inflammatory myopathy?

Very high CPK exceeding 10 times the normal limit Signup and view all the answers

Which factor does NOT indicate a higher likelihood of developing muscle disease in patients with amyopathic DM?

Presence of skin-limited disease only Signup and view all the answers

What is a common treatment for patients requiring additional immunosuppressive therapy?

Methotrexate Signup and view all the answers

What is a defining characteristic of inclusion body myositis (IBM)?

It is most common in those aged over 50 years Signup and view all the answers

Which aspect of juvenile dermatomyositis (JDM) is most true?

It can manifest primarily as skin disease Signup and view all the answers

What is NOT a possible symptom of antisynthetase syndrome?

Hepatic dysfunction Signup and view all the answers

During the management of relapses associated with rising CK levels, what does the presence of elevated CPK suggest?

Need for additional therapy Signup and view all the answers

What is the peak age of onset for dermatomyositis (DM)?

5 to 15 years and 45 to 65 years Signup and view all the answers

What is a characteristic skin lesion associated with dermatomyositis?

Heliotrope rash Signup and view all the answers

What is the typical muscle weakness pattern in polymyositis (PM)?

Symmetrical proximal muscle weakness Signup and view all the answers

Which antibody is strongly associated with interstitial lung disease in patients with dermatomyositis?

Antisynthetase (Jo-1) antibody Signup and view all the answers

What is an important component of the management for dermatomyositis?

Oral corticosteroids Signup and view all the answers

What is the female to male ratio in dermatomyositis (DM)?

1:1 Signup and view all the answers

Which screening test is recommended for patients diagnosed with dermatomyositis due to the increased risk of malignancy?

Chest CT scan Signup and view all the answers

Which of the following is a sign of severe muscle involvement in polymyositis?

Dysphonia Signup and view all the answers

What is a typical finding in muscle biopsy for patients with polymyositis?

Fiber necrosis and inflammatory cell infiltrate Signup and view all the answers

How does dermatomyositis vary in presentation compared to polymyositis?

Presence of distinctive skin lesions Signup and view all the answers

Study Notes

Idiopathic Inflammatory Myopathies (IIM)

IIM is a group of diseases causing muscle inflammation with no known cause.
Doctors use different methods to classify the various forms of IIM.
Adult-onset dermatomyositis (DM) and polymyositis (PM) are common IIMs.
A subtype of IIM is called overlap myositis which is associated with features of another connective tissue disease.
Immune-mediated necrotizing myositis (IMNM) is a type of IIM characterized by specific muscle damage.
Inclusion body myositis (IBM) is another type, differing in its muscle presentation from other types of inflammatory myopathies.
Juvenile dermatomyositis affects adolescents.

Differential Diagnosis of Myopathies

Diagnosing IIM involves excluding other conditions that may present similar symptoms, such as neuromuscular disorders, infectious myositis, muscular dystrophies, and various muscular disorders.
Bacterial and viral infections can cause muscle inflammation.
Metabolic myopathies such as glycogen storage disorders or nutritional deficiencies need to be considered.
Some endocrine conditions like hypothyroidism and hyperthyroidism can have muscle involvement.
Miscellaneous causes including sarcoidosis, organ failure, amyloidosis, or acute rhabdomyolysis need to be ruled out.
Immune-mediated necrotizing myositis (IMNM) is a distinct type of myositis.

Classification of IIM

Adult-onset DM
Adult-onset PM
Overlap myositis
Immune-mediated necrotizing myositis (IMNM)
Juvenile-onset DM (JDM)

Polymyositis and Dermatomyositis

These conditions frequently present with muscle weakness.
Muscle weakness, often starting in the proximal muscles, is a hallmark.
Unusual ocular and facial weakness warrants another diagnosis investigation.
Pain is often absent.

Dermatomyositis

Presents similarly to polymyositis and comes with skin lesions, which may include distinctive Gottron's papules, a heliotrope rash, and a shawl sign.
Skin lesions appear as scaly or purplish bumps on the extensor surfaces of the fingers and over the upper back, neck, and shoulders.

Clinical Features

Muscle weakness, often symmetrical and affecting proximal muscles first, is common.
Ocular and facial muscle weakness may be present but unusual and warrant further investigation.
Pain is usually absent or mild.
Pharyngeal muscle weakness leading to dysphonia and swallowing problems may indicate more severe disease.
Interstitial lung disease occurs in around 30% of cases.
Presence of antisynthetase antibodies is linked to interstitial lung disease.

Investigations

Creatine kinase (CK) levels are elevated and useful in monitoring disease activity.
Other enzymes like ALT, AST, and aldolase can also be elevated.
Electromyography (EMG) helps differentiate myopathy from other nerve disorders.
Magnetic resonance imaging (MRI) can facilitate muscle biopsy targeting.
Muscle biopsies are key to definitively diagnosing inflammation, regeneration, and infiltration of muscle tissue.
Screening for malignancy is a routine aspect of IIM management due to the threefold increased risk.

Management

Oral corticosteroids, such as prednisolone, are common initial treatments.
High-dose intravenous corticosteroids may be needed for severe cases.
Immunosuppressants like azathioprine, methotrexate, and others are used to help manage symptoms and prevent relapse.
Intravenous immunoglobulin may be used in refractory cases.

Differentiating Steroid Myopathy from IIM Exacerbation

Weakness while on prednisone warrants further investigation, particularly if prednisolone dosage is above 20mg/day.
Measuring CPK and aldolase can help distinguish, inflammation from muscle atrophy.
Muscle MRI can confirm ongoing inflammation.

Amyopathic Dermatomyositis

This subtype features skin manifestations without significant muscle involvement.
Approximately half of these patients may eventually develop muscle disease over time.

Antisynthetase Antibody (ASA) Syndrome

Proximal muscle weakness is commonly the initial manifestation.
Mechanic's hand, a skin lesion characterized by cracking and fissures on finger pads, particularly on the radial side of the index finger, is often associated.
Interstitial lung disease (ILD), arthritis, Raynaud's phenomenon, and fever may also occur.

Immune-mediated Necrotizing Myositis (IMNM)

Muscle disease is primarily seen in this type.
Symptoms range from acute to subacute progressive proximal muscle weakness accompanied by myalgias.
Creatine kinase (CPK) levels are very high, exceeding the normal range by 10 to 50 times.
Interstitial lung disease or skin involvement is generally absent.
Muscle histology reveals scattered necrotic fibers along with macrophages, with a minimal inflammatory infiltrate.

Inclusion Body Myositis (IBM)

Muscle disease is a prominent feature, usually presenting as proximal muscle weakness.
There tends to be more distal muscle involvement, and it is often asymmetrical, meaning the weakness affects one side more than the other.
Often, accompanying nerve damage is present.
Muscle biopsy is crucial for diagnosis, revealing myopathic features with CD8+ T-cell infiltration, red-rimmed vacuoles, and amyloid deposits.

Juvenile Dermatomyositis

It is the most frequent inflammatory myopathy in children and adolescents, not necessarily needing a search for malignancy.
Symptoms often mimic adult-onset dermatomyositis, with periods of remission and relapse.
Calcinosis, a calcium deposit in the skin, presents in about 30% of cases.

Case Scenarios

Various case examples outline how physicians analyze muscle weakness cases to arrive at particular diagnoses. Relevant laboratory results provide medical insight.

Epidemiology

Annual incidence of IIMs is relatively low.
The peak onset age is bimodal for Dermatomyositis (DM), with one peak between 5-15 years old, and another between 45-65 years.
Polymyositis (PM) typically peaks around 50-60 years old.
Generally, females are affected twice to three times more often than males.

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Description

This quiz covers the essential aspects of Idiopathic Inflammatory Myopathies (IIM) including its classification, common types such as dermatomyositis and polymyositis, and differential diagnosis. Test your knowledge on the various forms of muscle inflammation and associated conditions.