2. Inflammatory myopathies are rare diseases.
Incidence range from 2.2–7.7 cases per million.
Age at onset has a bimodal distribution with peaks
observed between ages 10 and 15 years in children and
between 45 and 60 years in adults.
3. Women are affected twice as commonly as men, with
the exception of inclusion body myositis, in which
men are affected more often.
4. Clinical Classification of the Idiopathic
Inflammatory Myopathies
Polymyositis
Dermatomyositis
Juvenile dermatomyositis
Myositis associated with neoplasia
Myositis associated with connective tissue disease
Inclusion body myositis
8. Clinical Features
Proximal and symmetric muscle weakness is the
cardinal clinical feature of the inflammatory
myopathies.
Weakness of the proximal muscles of the legs is
usually noted first and results in difficulty arising from
a chair or climbing stairs.
Weakness of the proximal arm muscles may limit the
ability to lift heavy items, to brush one's hair, or to
reach up to shelves.
9. The detection of muscle weakness on physical
examination typically relies on manual muscle
strength testing and is usually rated on a scale of 0 to
5.
Functional measurements of muscle strength are often
helpful.
These include determining how long it takes the
patient to arise ten times from a chair without use of
the arms or to walk 10 meters. The patient's ability to
rise from a squat or stand on his or her toes and heels
can also be assessed
10.
11. Pelvic and shoulder girdle musculature are affected
most, but weakness of neck muscles, particularly the
flexors, is also common.
Ocular and facial muscles are virtually never involved.
Dysphagia may develop secondary to esophageal
dysfunction or cricopharyngeal obstruction.
12. Pharyngeal muscle weakness may cause dysphonia and
difficulty swallowing.
Pulmonary and cardiac manifestations may precede
the onset of muscle weakness or develop at any time
during the course of disease.
13.
14.
15. The clinical features of dermatomyositis include all those
described for polymyositis plus a variety of cutaneous
manifestations.
Two cutaneous manifestations are considered
pathognomonic.
1. Gottron papules (symmetric lacy pink or violaceous
raised lesions typically found on the dorsal and lateral
aspects of the interphalangeal and metacarpophalangeal
joints)
2. Gottron sign (symmetric macular violaceous erythema
overlying the dorsal aspects of the interphalangeal and
metacarpophalangeal joints, olecranon processes,
patellae, and medial malleoli)
18. Characteristic cutaneous findings :
1. Heliotrope (violaceous) discoloration of the eyelids.
2. Macular erythema of the posterior shoulders and
neck (shawl sign).
3. Anterior neck and upper chest (V sign).
4. Dystrophic cuticles; and
5. Periungual telangiectases and nailfold capillary
changes.
19. Heliotrope rash of dermatomyositis demonstrating both erythema
and diffuse periorbital edema.
21. V-neck rash in a patient with dermatomyositis demonstrating
photosensitive nature over anterior chest.
22. “Shawl sign” in a patient with dermatomyositis featuring an
erythematous rash across the upper back and extending onto the neck
in the
distribution of where a shawl is worn.
23. Cuticular overgrowth with periungual erythema and capillary
dilatation in a patient with dermatomyositis.
24. "Mechanic's hands" refers to darkened or dirty-
appearing horizontal lines and fissures that are seen
across the lateral and palmar aspects of the fingers.
This skin lesion can be seen in both dermatomyositis
and the anti-synthetase syndrome subset of
polymyositis.
25. Mechanic’s hands. Note the erythema and hyperkeratotic changes
and cracking of the skin on the lateral aspects of the fingers in this
patient with the anti-Jo-1 autoantibody.
28. In juvenile dermatomyositis, the skin lesions and
weakness are almost always coincidental, but the
severity and progression of each varies greatly from
patient to patient.
Juvenile variant differs from the adult form because of
the coexistence of vasculitis, ectopic calcification, and
lipodystrophy.
30. Gastrointestinal ulcerations resulting from vasculitis
can cause hemorrhage or perforation of a viscus.
Ectopic calcification may occur in the subcutaneous
tissues or in the muscles.
31.
32.
33.
34. Amyopathic dermatomyositis : Biopsy-confirmed,
classic cutaneous findings of dermatomyositis have
normal muscle strength, muscle enzymes,
electromyograms (EMGs).
Dermatomyositis sine myositis: Above findings plus
normal muscle histology
35.
36. Muscle weakness associated with an underlying
malignancy develops in a subset of patients with
inflammatory myopathies.
Malignancy may precede, or develop after, the onset of
muscle weakness, usually the two are diagnosed within a 1-
year period.
The sites or types of malignancy that occur in association
with myositis are those that are expected for the age and
gender of the patient.
37. Inclusion body myositis mainly affects persons over
the age of 50 years .
It affects men twice as often as women.
Symptoms are often present for 5–8 years before the
diagnosis is made.
Predominant weakness of the quadriceps, long finger
flexors, and anterior calf muscles is characteristic.
38. Laboratory Findings
An abnormal creatine kinase (CK) level is possibly the
most sensitive indicator of skeletal muscle damage.
Normal levels of CK may be found
1. Very early in the course of polymyositis.
2. Dermatomyositis.
3. In advanced cases with significant muscle
atrophy.
4. In myositis associated with a malignancy.
5. Inclusion body myositis.
39. Tests of acute phase reactants, the erythrocyte
sedimentation rate and C-reactive protein levels, are
abnormal in only some patients with myositis.
The erythrocyte sedimentation rate is normal in about
half of patients with polymyositis and is elevated
above 50 mm/h (Westergren method) in only 20%.
40. Certain autoantibodies are found almost exclusively in
patients with idiopathic inflammatory myopathies,
and therefore are termed myositis-specific
autoantibodies .
Antinuclear antibodies (ANAs) may be found in the
serum of over 50% of patients with inflammatory
muscle disease
41.
42. Most myositis-specific autoantibodies are directed
against amino acyl-tRNA synthetase activities.
The most common of these is anti-histidyl-tRNA
synthetase (Jo-1), present in approximately 20% of
patients with polymyositis
43. Patients with these autoantibodies typically manifest
myositis (polymyositis more commonly than
dermatomyositis) plus several extramuscular features
including interstitial lung disease, arthritis,
mechanic's hands, and Raynaud phenomenon.
The combination of these features and an
inflammatory myopathy has been termed
"antisynthetase syndrome."
44. EMG
EMG is quite effective for :
1. Differentiating between myopathic and neuropathic
conditions.
2. Localizing a neurologic lesion to the central nervous
system, spinal cord anterior horn cell, peripheral nerves,
or neuromuscular junction.
3. In addition, knowledge of the distribution and severity
of abnormalities can guide selection of the most
appropriate site to biopsy if MRI is not available.
45. In polymyositis and dermatomyositis, EMG classically
reveals the following triad:
1. Increased insertional activity, fibrillations, and
positive sharp waves.
2. Spontaneous, bizarre high-frequency discharges.
3. Polyphasic motor unit potentials of low amplitude
and short duration.
46. Muscle histology
In classic polymyositis, muscle biopsies reflect a T-cell
mediated autoimmune process.
The lymphocytic cell infiltrate is found predominantly
in endomysial locations.
T lymphocytes, especially CD8+ cytotoxic T cells, can
be seen surrounding and invading non-necrotic fibers
expressing class I major histocompatibility antigen.
47. The muscle biopsy in inclusion body myositis closely
resembles that of polymyositis, with endomysial
inflammatory infiltrates and CD8+ T-cell invasion of non-
necrotic muscle fibers.
However, a characteristic feature of inclusion body myositis
is the presence of intracellular vacuoles.
The vacuoles contain basophilic (red on Gomori trichrome
stain) granules in their center or along their walls, leading
to their "red-rimmed" appearance.
48. Treatment
Glucocorticoids are the standard first-line medication
for any idiopathic inflammatory myopathy.
Initially, prednisone is usually given in a single dose of
1 mg/kg/d, but in severe cases, the daily dose can be
divided or intravenous methylprednisolone can be
used.
49. If a patient does not respond to glucocorticoid therapy,
another agent is added, usually either azathioprine or
methotrexate.
Intravenous immune globulin is often beneficial in the
treatment of dermatomyositis and polymyositis, but
its effect is short-lived and repeat infusions are
generally necessary every 6–8 weeks.
50. Other immunosuppressive agents or therapeutic modalities
have been used in treatment-resistant patients, including
1) Cyclophosphamide,
2) Cyclosporine
3) Tacrolimus
4) Rituximab
5) Etanercept
6) Infliximab
7) Mycophenolate mofetil
8) Plasmapheresis
9) Total-body (or total-nodal) irradiation.
