Inflammatory Myopathies
Dipika Aggarwal, MD
PGY 4 Neurology
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Idiopathic Inflammatory Myopathies
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Dermatomyositis (DM)
Polymyositis (PM)
Autoimmune Necrotizing Myopathy (NM)
Inclusion Body Myositis (IBM)
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Idiopathic Inflammatory Myopathies
Epidemiology
• Annual incidence – 1:100,000
• Incidence of individual myositides has been limited by the different
diagnostic criteria employed in various epidemiological studies
• IBM is the most common myopathy after age 50 with prevalence of
3.5/100,000 cases
• Disease of adults (except for Juvenile DM)
• Women are more commonly affected
• Genetic predisposition secondary to inherited Human Leukocyte Antigens
(HLA) haplotypes
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Idiopathic Inflammatory Myopathies
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Idiopathic Inflammatory Myopathies
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Dermatomyositis (DM)
• Can present at any age, including infancy
• Affects female more than males
• Acute (over several weeks) or insidiously (over months) progressive,
painless, proximal weakness with or without characteristic skin rash
• Proximal leg and arm muscles are usually the earliest and most severely
affected muscle groups
• Mostly painless
• Speech, chewing and swallowing difficulties may be seen
• JDM commonly presents after a febrile episode and with a skin rash
• Multisystem involvement is more common in JDM
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Dermatomyositis : Skin involvement
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Distinct rash
Occurs before or with the onset of muscle weakness
Variable degree of muscle versus skin involvement
Amyopathic DM– isolated rash with no muscle involvement
Adermatopathic DM – isolated myositis
Classical DM findings:
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heliotrope rash
Gottron’s papules
dilated nail bed capillaries
V-sign
shawl sign
mechanic’s hands
• Subcutaneous calcinosis seen in 30-70% cases of JDM, less common in
adults
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DM : Skin findings
Heliotrope rash: purplish discoloration along the
hairline of scalp and malar region of the face and
eyelids
Dilated capillary loops evident in the nail bed as
well as small ulceration involving the distal aspect
of the little finger
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DM : Skin findings
Gottron papules : erythematous lichenoid papular scaly rash, over the extensor surface of the hands and fingers
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DM : Skin findings
V sign: Erythematous rash around face, neck and
anterior chest
Shawl sign: erythematous rash affecting upper back
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DM : Skin findings
Mechanic’s hands: Cracking of the finger pad skin, commonly involving the first, second, and third fingers
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Dermatomyositis – Lab features
• Serum CK
– Elevated serum CK with levels ranging upto 50 times the upper limit of normal
– CK level may be normal in less than 10% pts
– Do not co-relate with the severity of weakness
• ANA is detected in 24-60% of pts with DM
• Myositis specific antibodies
– Found in a minority of patients
– Useful in predicting response to therapy and prognosis
– Cytoplasmic antibodies directed against transitional proteins (tRNA synthetases and
anti-signal recognition particle)
– Directed against nuclear proteins (Mi-2 and Mas antigens)
– Most common MSA are Jo-1 antibodies, associated with Interstitial Lung Disease, seen in
20% pts (MTX should be avoided)
– Mi-2 antibodies (15-20% DM pts); associated with acute onset, florid rash, good
response to therapy and favourable prognosis
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Dermatomyositis - Electrophysiology
• Motor and sensory nerve conduction studies are mostly normal
• Needle examination shows non specific findings of irritative myopathy
(increased insertional activity, fibrillation potentials and positive sharp
waves, complex repetitive discharges)
• Muscle fibrosis in advanced cases may result in reduced insertional
activity due to fibrosis
• Motor unit action potentials (MUAPs) are polyphasic, brief, and of low
amplitude
• EMG is helpful in assessing relapsing weakness during treatment
• Worsening strength in the absence of fibrillation potentials suggests a
steroid induced myopathy
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Dermatomyositis
Histopathology and Pathogenesis
• Histology
– Earliest finding : Membrane Attack Complexes around blood vessels
– Pathognomic : perifascicular atrophy with or without perimysial and
perivascular inflammatory infiltrate (macrophages , B cells , CD4+ T cells ,
plasmacytoid dendritic cells)
– Electron microscopy: tubulo reticular inclusions in the intramuscular
arterioles and capillaries
• Pathogenesis
– Humorally mediated micro angiopathy
– antibodies directed against endothelial cells activate complement factors 
membrane attack complex (MAC) deposition on capillaries  endothelial
damage, capillary necrosis, perivascular inflammation, ischemia and myofibril
necrosis
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Muscle Biopsy
Perifascicular atrophy with perimysial inflammation
MAC deposition around blood vessels
(Immunoperoxidase stain)
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Muscle Biopsy
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Idiopathic Inflammatory Myopathies
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Polymyositis (PM)
• Exclusionary diagnosis in pts who do not have a rash or alternate muscle
or nerve disease
• PM is a disease of adults over age 20 years
• More prevalent in female
• Subacute to insidiously progressive, proximal arm and leg weakness
• Myalgias and tenderness are common but usually not the first presenting
symptoms
• Dysphagia is seen in one-third of patients
• Facial weakness is occasionally present
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Polymyositis – work up
• Elevated CK in range of 5 to 50 times the normal. Unlike DM, CK is always
elevated in PM
• Positive ANA (16-40% )
• Myositis specific antibodies
– useful in predicting response to therapy and prognosis
– Anti SRP antibodies: severe, fulminant, steroid resistant PM
– Anti Jo-1 antibodies: associated with ILD
• Electro diagnostic tests show evidence of muscle irritation
– Increased insertional activity, positive sharp waves, polyphasic MUAPs
– Do not distinguish PM from other IIM
• Skeletal muscle MRI – increased signal consistent with muscle edema and
inflammation
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Polymyositis
Histopathology and Pathogenesis
• Histology
– fiber size variability
– scattered necrotic and regenerating fibers
– endomysial inflammation consisting of cytotoxic T cells and macrophages
• Pathogenesis
– HLA- restricted, antigen specific, cell mediated immune response directed
against muscle fibers
– ?? Trigger
• viral infections (inconclusive hypothesis)
• MHC 1 expressed endogenous peptide “auto antigen”  activation of CD8+ cytotoxic T
cells and macrophages that invade myocytes  destroy muscle fibres through perforin
pathway causing pore formation and osmolysis
– Unlike DM - MAC, complement or immuno globulins are not deposited on the
microvasculature in PM
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Muscle Biopsy
Endomysial inflammatory cell infiltrate surrounding and invading non necrotic muscle fibres
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Idiopathic Inflammatory Myopathies
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Autoimmune Necrotizing Myopathy (NM)
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Increasing recognized autoimmune myopathy
little or no inflammatory infiltrate
more common in females
sub acute progressive proximal weakness without rash
rapid onset than PM; markedly severe in 30% cases
myalgia and dysphagia
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Autoimmune Necrotizing Myopathy
Subtypes
• Paraneoplastic NM
– rare, rapidly progressive
– severe variant
– associated with adenocarcinoma
• NM with thick “pipestem”
capillaries
– associated with subacute weakness
– brain infarction due to vascultis
– Connective Tissue Disease
• SRP autoantibodies associated
NM
– Severe, fulminant
– treatment refractory
– cardiac complications (myocarditis)
• Statin induced autoimmune NM
(SANAM)
– affects between 46 to 89 year old pts
– onset may be delayed upto 10 yrs
following statin initiation
– may occur several months after
discontinuation
– Often therapy resistant
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Autoimmune Necrotizing Myopathy – work up
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Elevated CK – more than 10 times the normal
Positive ANA – suggestive of underlying CTD
MSA – SRP autoantibodies
EMG – irritative myopathy
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NM - Histopathology and Pathogenesis
• Histology
– Scattered necrotic myofibers with myophagocytes
– Absence or paucity of T-lymphocytic inflammation
– Unlike DM, perivascular inflammation is scant, and there are no endothelial tubulo
reticular inclusions
– Thick-walled and enlarged “pipestem” capillaries is diagnostic of NM with pipestem
capillaries
– SRP-associated NM: bimodal distribution of fiber sizes, increased endomysial connective
tissue, and reduced endomysial capillary number with enlargement and thickening
• Pathogenesis
– Unknown
– deposition of complement MAC on small arterioles and capillaries with thickened
endothelial walls suggests humorally mediated microangiopathy
– Anti 200/ 100 antibodies
• Autoantigen is 3-hydroxy -3- methylglutaryl-coenzyme A reductase (HMGCR)
protein
• Statin upregulate HMGCR protein levels, thus triggering anti- HMGCR auto
immunity
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Muscle Biopsy
Scattered necrotic fibers, some undergoing phagocytosis
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Associated conditions
• There is an increased incidence of interstitial lung disease, autoimmune
disorders, cancer and cardiac disorders in patients with DM , PM and NM
• Cardiac
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conductions defects, arrhythmias
ventricular and septal wall motion abnormalities
Pericarditis and congestive heart failure (less common)
Myocarditis (seen in 1/3rd pts), associated SRP autoantibodies
• Pulmonary
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10-25% of patients have ILD
Jo-1 antibodies are present in at least 50% of ILD cases
Prompt chest imaging and pulmonary function tests
Pulmonary consultation
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Associated conditions (contd.)
• Malignancy
– Most studies suggest 15 to 25% of adult DM patients, older than 40 years,
have preexisting, concurrent, or future malignancies
– Most common DM-associated malignancy
• Women: ovarian cancer
• Men: small cell lung cancer
– Other common malignancies are – pancreatic cancer, stomach and colorectal
cancers and lymphoma
– Rarely, malignancy has been reported in JDM
– Malignancy is increased in PM and NM when compared with the general
population
– Routine screening with careful skin examination for melanoma; CT scan of
chest, abdomen and pelvis; and in women, mammogram and pelvic exam; in
men, testicular and prostate examinations
• If primary screening is negative, repeat screening is recommended after 36 months; thereafter every 6 months for 4 years
– Treatment of the malignancy improves muscular involvement
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Associated conditions (contd.)
• Gastro-intestinal system
– Dysphagia, aspiration and delayed gastric emptying due to smooth and skeletal
muscle weakness
– Vasculopathy affecting the GI tract may cause bowel ischemia, necrosis and
perforation more commonly seen in JDM
• Joints
– Polyarthritis has been reported in up to 45% of patients with PM
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Treatment
Immunosuppressive therapy is the mainstay of treatment
First line
Second line
Third line/ Emerging drugs
• Prednisone
• IV Methylprednisone
• Methotrexate
• Azathioprine
• Intravenous Immunoglobulins
• Mycophenolate
• Cyclosporine
• Tacrolimus
• Rituximab
• Etanercept
• Cyclophosphamide
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First line: Corticosteroids
• No controlled trails
• Usual dosing schedule
– 1mg/kg/day or 60-100mg daily for 2-4 weeks followed by every other day schedule
– Slower taper in more severe disease
– Intravenous steroids may be used in more severe cases initially followed by a slower
taper
• response to therapy seen in 2-3 months
• no improvement is seen in 4-6 months or concerns for side effects or
exacerbation during the taper , add second line agents
• Special points
– CXR, PPD – screening; if PPD positive initiate Rx with isoniazid
– DEXA at baseline and every 6 months; if bone density < 1.0 SD initiate Rx with
alendronate
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Second line of management
Steroid sparing agents
Methotrexate
- Antifolate drug; inhibits lymphocyte proliferation
- Initial dose of 7.5mg weekly, upto 25mg per week; therapeutic effect after 4-8 weeks
- Side effects : myelosuppression, liver/ renal toxicity, interstitial pneumonitis, stomatitis, teratogenicity
- Contra indications: Presence of Anti Jo-1 antibodies or ILD, severe renal/ hepatic impairement,
pregnancy
- Special points: folate co-administration, monitor CBC and LFT routinely, monitor PFTs at baseline and
every 6 months
Azathioprine
- Antimetabolite; blocks T cell proliferation
- Usual dose: 2 to 3 mg/kg/day ranging from 100 to 250mg / day
- Delayed therapeutic response, 4-8 months (peaks at 1-2 years)
- Side effects: myelosuppression, liver toxicity, acute hypersensitivity reaction/ flu like illness (12%),
pancreatitis, teratogenicity
- Contra indications: Pregnancy
- Special points: monitor CBC and LFT every 2 weeks until stable dose, then once monthly; if leukopenia
then decrease dose; if LFTs elevated x2 then discontinue
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Second line of management
Steroid sparing agents
Intravenous Immunoglobulins
- complex immuno modulatory mechanism of action: reduced autoantibody production and binding,
suppression of pro inflammatory cytokines
- AAN guideline recommend IVIg as possibly effective for non responsive DM
- Dose: initial dose of 2 g/kg divided over 2 to 5 days. Maintenance dosing of 0.4 to 2 g/kg per month
administered every 1 to 4 weeks
- Side effects: Flu like illness, headache, aseptic meningitis, risk of renal failure and thrombosis
- Contra indications: Immunoglobulin A deficiency, renal insufficiency, significant atherosclerotic disease
- Special points: very expensive
Mycophenolate mofetil
- Inhibits proliferation of T and B lymphocytes by blocking purine synthesis
- Dose: 1 to 1.5gm twice daily
- Side effects: myelosuppression, diarrhea, HTN, tremor
- Contra indications : myelosuppression, pregnancy
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Third line
• Cyclosporine
– Dose: 3 to 4 mg/kg per day; max
6mg/kg/day
– C/I: HTN, renal dysfunction,
malignancy, pregnancy
– S/E: HTN, renal failure, gingival
hyperplasia, GI upset
– Monitor BP, renal function, drug level
• Tacrolimus
– Dose: 2mg oral titrated to clinical
response/ tolerance
– C/I: ILD and Anti Jo-1 antibodies,
renal/ hepatic impairement
– S/E: diarrhea, headache, tremors,
insomnia, lymphoma
• Cyclophosphamide
– Dose: 1-2mg/kg per day
– C/I: myelosuppression, pregnancy
– S/E: hemorrhagic cystitis, alopecia, GI
upset
– High fluid intake, monitor UA and
CBC closely
• Recent drug trials
– Etanercept
– Rituximab
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Recent drug trials
Randomized, Pilot Trial of Etanercept in Dermatomyositis; Muscle
Study Group (Amato, et al) Neurology 2011
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Etanercept: Tumor necrosis factor α inhibitor
Randomized, double blind, placebo controlled trial
16 subjects randomized: 11 – etanercept; 5 – placebo
Duration of study: 52 weeks
Etanercept: 50 mg subcutaneous weekly
All subjects tapered off prednisone over 24 weeks
Outcome measures: adverse events, time from randomization to failure, average
prednisone dose at 24 weeks
Results:
– All 5 Placebo subjects: failed (median 148 days)
– 6/11 Etanercept subjects: failed (median 358 day)
– 5/11 Etanercept subjects: successfully tapered off Prednisone
– Average prednisone dosage after 24 weeks lower in etanercept group
(1.2mg/day) as compared to placebo group (29.2mg/day)
Conclusion: Etanercept may have steroid sparing effect; need further study
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Recent drug trials
Rituximab in the Treatment of Refractory Adult and Juvenile Dermatomyositis
and Adult Polymyositis. Oddis et al, 2011
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Rituximab: B cell depleting agent
Randomized, double blind, placebo phase trial
195 subjects with refractory disease (76 PM, 76 DM and 48 JDM)
Duration of study: 44 weeks
2 groups:
– Group A ( Rituximab early)
– Group B ( Rituximab started 8 weeks later)
Outcome measures:
– Primary end point: time to achieve definition of improvement
– Secondary end point: time to achieve 20% improvement in muscle strength
Results
– No significant difference in Group A and B in primary end point (20.2 and 20 weeks
respectively)
– No difference in secondary end point
– 83% of subjects met the primary end point/ DOI following Rituximab treatment
Conclusion: The role of B cell depleting therapies in myositis warrants further study
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Other therapies
• Diet and lifestyle
– Dietary supplementation has limited role
– Oral creatine may be of potential benefit
• Assistive devices
– Single prong cane, Rolling walker, wheelchair to prevent falls
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Physical therapy
– To maintain strength and address ADLs
– Early mobilization to prevent flexion contractures of large joints
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Prognosis
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The prognosis of the idiopathic inflammatory myopathies is generally favorable
Overall, drug-free remissions are rare except in JDM
Poor prognostic factors
– old age
– male gender
– non-Caucasian ethnicity
– longer symptom duration
– ILD, cardiac involvement
– associated malignancy
– dysphagia
– serum MSA (anti Jo-1 antibodies, anti SRP antibodies)
Mortality remains two- to three fold higher than the general population; with
cancer, lung, cardiac complications, and infections being the most common causes
of death
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Idiopathic Inflammatory Myopathies
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Inclusion body myositis (IBM)
• Most common inflammatory myopathy after age 50 yrs
• Insidious onset, slowly progressive proximal leg and distal arm weakness
• Delayed diagnosis with average duration of symptoms prior to diagnosis is
6-7 yrs
• Male are affected more than female
• Hallmark: weakness and atrophy (2/3rd of the pts)
– Legs: knee extensors, ankle dorsiflexors
– Arms: wrist and finger flexors
• Upto 82% of patients have marked asymmetry
• Sparing of thenar and hypothenar muscles helps distinguish IBM from ALS
• Dysphagia occurs on 70% patients
• Mild to moderate facial weakness
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IBM
marked difficulty in flexing the fingers of the left
hand as compared to the right
Quadriceps atrophy
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IBM – work up
• Serum CK may be normal or elevated up to 10 times normal
• ANA positive in 20% patients
• Nerve conduction studies - mild sensory axonal peripheral polyneuropathy
in up to 30% of patients with IBM
• Needle examination - evidence of muscle irritation (increased insertional
activity, positive sharp waves, polyphasic potentials)
• Skeletal muscle MRI scans – atrophy and signal abnormalities in affected
muscle groups
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IBM - Histopathology and Pathogenesis
• Histology
– Endomysial inflammation
– Small group of atrophic fibers
– Eosinophilic cytoplasmic inclusions ( better visualized with
immunostain directed against phosphorylated tau)
– Multiple myofibers with one or more rimmed vacuoles lined with
granular material (likely amyloid deposition-Congo Red stain)
• Pathogenesis ; unknown
– Autoimmune - presence of inflammatory cells on histology (cytotoxic T
cells, myeloid dendritic cells, B cells and IBM autoantibody)
– Degenerative - no response to immunotherapy, presence of protein
aggregates (amyloid, hyperphosphorylated tau, neurofilament heavy
chain) within rimmed vacuolated muscle fibers
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Muscle Biopsy
H&E stain
Vacuole filled with granules (Modified Gomori
trichrome stain)
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Treatment
• Refractory to all treatments
• Various RCT of IVIg with or w/o steroids, MTX, beta interferon, etanercept
did not show any benefit
• Some patients may have transient and mild improvement with
corticosteroids and exercise therapy early on in the course of the disease
• Several novel therapies are being evaluated – lithium chloride,
arimoclomol, follistatin gene transfer therapy
• Arimoclomol: potent heat shock protein 70 inducer
– Inducing HSP levels may reverse the toxic cellular changes
– Recent two-center trial (KU and University College London) was conducted to
assess the safety and tolerability of Arimoclomol in IBM as compared to
placebo over 4 months of treatment
– Arimoclomol is well tolerated in this study population
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Prognosis
• Associated conditions
– Unlike DM &PM, IBM is not
associated with myocarditis,
lung disease and malignancy
– 15% pts have underlying
autoimmune CTD like SLE,
Sjogren’s, Scleroderma and
sacrcoidosis
• Prognosis
– Life expectancy not
significantly altered
– Most patients are wheelchair
bound by 10-15 years
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References
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Dimachkie MM, Barohn RJ. Idiopathic inflammatory myopathies. Semin Neurology 2012;
32:227-236
Dimachkie MM, Barohn RJ. Inclusion Body Myositis. Semin Neurology 2012; 32:237-245
Dimachkie MM. Idiopathic Inflammatory Myopathies. Journal of Neuroimmunology 231
(2011): 32-42
Amato AA, Russell JA. Inflammatory Myopathies. Neuromuscular Disorders 2008; Chapter 30:
681-713
Distad BJ, Amato AA. Inflammatory myopathies. Current Treatment Options in Neurology
(2011) 13: 119-130
Oddis CV, Reed AM. Rituximab in the Treatment of Refractory Adult and Juvenile
Dermatomyositis and Adult Polymyositis. Athritis and Rheumatism, 2013, Vol 65, 314-324
Amato AA. Randomized, Pilot Trial of Etanercept in Dermatomyositis; Muscle Study Group.
Neurology 2011; 70: 427-436
Dalakas MC, Hohlfeld R. Polymyostis and Dermatomyositis. The Lancet 2003; Vol 362: 971982
Titulaer MJ, Soffietti R, Dalmau J, et al. Screening for tumours in paraneoplastic syndromes:
report of an EFNS task force. Eur J Neurol 2011;18(1):19–e3
Amato AA, Barohn RJ. Evaluation and treatment of inflammatory myopathies. J Neurol
Neurosurg Psychiatry 2009; 80: 1060 – 1068
http://neuromuscular.wustl.edu
Miller FW. Myositis-specific autoantibodies: touchstones for understanding the inflammatory
myopathies. JAMA 1993;270:1846-1849
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