Inflammatory Myositis

 

NOTES

OSMOSIS.ORG

NOTES

INFLAMMATORY MYOSITIS

▪ Multiple disorders involving autoimmune

infl ammation, injury of skeletal muscles

▪ Most commonly include polymyositis,

dermatomyositis, inclusion body myositis

▫ Dermatomyositis predominantly

mediated by humoral immune response;

polymyositis, inclusion body myositis by

cellular immune response

RISK FACTORS

▪ Age (more common in older population)

▪ Dermatomyositis, polymyositis more

common in individuals who are biologically

female

▪ Inclusion body myositis more common in

individuals who are biologically male

▪ Chronic viral infections: human T cell

lymphotropic virus Type I (HTLV-1), HIV

▪ Autoimmune diseases

▪ Malignancies

COMPLICATIONS

▪ Dysphagia, pulmonary involvement

▪ Cardiovascular involvement

PATHOLOGY & CAUSES

▪ Proximal muscle weakness

▪ Inclusion body myositis

▫ Distal muscle weakness

▪ Dermatomyositis

▫ Skin rashes

SIGNS & SYMPTOMS

LAB RESULTS

▪ ↑ muscle enzymes, like creatine kinase (CK)

▪ Muscle biopsy

▫ Dermatomyositis: perivascular,

perimysial infl ammation

▫ Polymyositis: endomysial infl ammation

▫ Inclusion body myositis: endomysial

infl ammation, intracytoplasmic vacuoles

with protein depositions

OTHER DIAGNOSTICS

▪ Physical examination

▫ Muscle weakness

Electromyography (EMG)

▪ Pathological signals

DIAGNOSIS

MEDICATIONS

▪ Corticosteroids, immunosuppressive agents

OTHER INTERVENTIONS

▪ Physical rehabilitation

TREATMENT

GENERALLY, WHAT IS IT?

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653

Figure 113.1 A heliotrope rash affecting the

eyes of an individual with dermatomyositis.

Figure 113.2 Gottron’s papules on the

extensor surfaces of an individual with

dermatomyositis.

osms.it/dermatomyositis

DERMATOMYOSITIS

▪ Autoimmune disorder leading to

destruction of small blood vessels in

muscles, skin

▪ Unknown factor activates C3 protein

(complement component 3) → formation

of membrane attack complex (MAC),

accumulation in capillaries → destruction of

capillary wall → microinfarctions

▪ Juvenile: around seven years; associated

with calcinosis (deposition of calcium in

skin)

▪ Adult: > 40; associated with malignancy,

treating malignancy may cure myositis

RISK FACTORS

▪ > 60 years

▪ Malignancy

COMPLICATIONS

▪ Respiratory muscle weakness; dysphagia

(if esophagus, pharyngeal muscles

involved); interstitial pulmonary disease;

cardiovascular involvement

PATHOLOGY & CAUSES

▪ Weakness starts in proximal muscles,

slowly progresses (e.g. diffi culty getting up)

▪ Heliotrope rash

▫ Purplish eyelids with posible periorbital

edema

▪ Gottron papules

▫ Scaling erythema of knuckles, elbow,

knees

▪ V-shaped rash on chest

SIGNS & SYMPTOMS

DIAGNOSTIC IMAGING

CT scan

▪ Malignancy suspected

LAB RESULTS

▪ Blood tests

▫ ↑ CK (muscle cells death)

▫ ↑ aspartate aminotransferase (AST)

DIAGNOSIS

654 OSMOSIS.ORG

▫ ↑ lactic dehydrogenase (LDH)

▫ Antinuclear antibodies (ANA)

▫ Anti-Mi-2 antibodies (acute phase,

better prognosis)

▪ Biopsy

▫ Perivascular, perimysial infl ammation

▫ Perifascicular atrophy

▫ “Ghost fi bers” (destroyed fi bers, can no

longer be stained)

OTHER DIAGNOSTICS

EMG

▪ Abnormal signals

MEDICATIONS

▪ Corticosteroids (e.g. glucocorticoid)

▪ Immunosuppressive agents (e.g.

methotrexate)

▪ IV immune globulins

TREATMENT

Figure 113.3 The histological appearance

of the skeletal muscle of an individual with

dermatomyositis. The perimysium and

endomysium have been infi ltrated by chronic

infl ammatory cells, with predilection for the

perimysium.

OTHER INTERVENTIONS

▪ Physical therapy (preserve muscle strength)

▪ Sunscreen, avoid sun exposure (in skin

disease)

osms.it/inclusion-body-myositis

INCLUSION BODY MYOSITIS

▪ Idiopathic infl ammation of muscles leading

to weakness, muscle atrophy

▪ Infl ammation, degenerative processes

▪ Unknown factor causes myofi bers to

present major histocompatibility complex

class I (MHC I) → CD8+ T cells gather,

recognize MHC I, bind → express perforin

→ pores form on myofi bers membranes →

cell degeneration

▪ Accumulation of abnormal amyloidogenic

proteins (e.g. beta-amyloid), cytotoxic effect

▫ Causes: misfolding of proteins;

damaged/inhibited proteasomes;

endoplasmic reticulum stress

PATHOLOGY & CAUSES RISK FACTORS

▪ Age > 50

▪ Chronic viral infections: HTLV-1

▪ Autoimmune diseases: Sjögren’s syndrome

COMPLICATIONS

▪ Dysphagia (if esophagus, pharyngeal

muscles involved)

▪ Slowly progressive muscle weakness,

sometimes asymmetric

▫ Proximal leg muscles (diffi culty getting

up, frequent falls)

▫ Distal arm muscles (weak grip)

SIGNS & SYMPTOMS

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LAB RESULTS

▪ Mild ↑ muscle enzymes (e.g. CK)

▪ Muscle biopsy

▫ CD8+ T lymphocytes, macrophages

infi ltrating non-necrotic myofi bers

▫ Vacuoles with amyloides, other protein

accumulations (inclusion bodies)

▫ ↑ MHC I on immunostaining

OTHER DIAGNOSTICS

▪ Clinical presentation

▫ Muscle weakness

EMG

▪ Polyphasic motor unit action potentials

(MUAPs) with small amplitude, short

duration

DIAGNOSIS

MEDICATIONS

▪ Immunosuppressive therapy

▫ Administered when another systemic

autoimmune disease present

OTHER INTERVENTIONS

▪ Physical therapy

▫ Muscle strengthening

▪ Speech therapy

▫ If dysphagia present

▪ Occupational therapy

TREATMENT

Figure 113.4 Gomori staining highlights the

rimmed vacuoles in inclusion body myositis.

▪ As disease progresses

▫ ↑ muscle atrophy

▫ ↓ deep tendon refl exes

Figure 113.5 A histological section of muscle

showing a myofi ber vacuole in an individual

with inclusion body myositis.

656 OSMOSIS.ORG

▪ Symmetrical weakness of proximal leg, arm

muscles (e.g. diffi culty climbing stairs)

▪ Neck fl exor weakness

▪ Mild myalgia, tenderness

▪ Dysphagia (if esophagus, pharyngeal

muscles involved)

SIGNS & SYMPTOMS

osms.it/polymyositis

POLYMYOSITIS

▪ Infl ammatory destruction of muscles

leading to muscle weakness

▪ Unknown factor induces CD8+ T cells,

macrophages to recognize nuclear,

cytoplasmic antigens of muscle cells →

immune cells surround nonnecrotic muscle

cells → muscle cell destruction

RISK FACTORS

▪ Autoimmune disease

▪ Chronic viral infection (HIV, HTLV-1)

COMPLICATIONS

▪ Aspiration pneumonia

▪ Interstitial lung disease

▪ Dysphagia → malnutrition, anorexia

PATHOLOGY & CAUSES

DIAGNOSTIC IMAGING

Chest X-ray, CT scan

▪ Pulmonary involvement

LAB RESULTS

▪ Blood tests

▫ ↑ CK, aldolase; ANA; antisynthetase

antibodies (anti-Jo-1)

▪ Muscle biopsy

▫ Endomysial infl ammation; intact blood

DIAGNOSIS

vessels; myofi bers surrounded by CD8+

T lymphocytes, macrophages

OTHER DIAGNOSTICS

▪ Physical examination

▫ Muscle weakness, tenderness

EMG

▪ Low amplitude, short duration potential;

repetitive discharges

Figure 113.6 A muscle biopsy from

an individual with polymyositis. The

lymphocytes penetrate individual myofi bers.

In this example, the infl ammation has

progressed to phagocytic destruction by

macrophages.

MEDICATIONS

▪ Corticosteroids

▪ Immunosuppressive agents (if

nonresponsive to corticosteroids)

▪ IV immune globulins (if severe, lifethreatening)

OTHER INTERVENTIONS

▪ Physical therapy (preserve muscle strength)

TREATMENT

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