Updated: 7/10/2019

Dermatomyositis / Polymyositis

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Snapshot
  • A 49-year-old woman with polymyositis presents to her physician’s office for weakness. She reports that she feels unusually tired and weak. She works as a makeup artist and in the past few weeks has experienced difficulty applying makeup on her clients. She finds it difficult to work while she has her arms raised. She denies any fevers, weight gain or loss, or any other motor deficits. Physical exam reveals decreased strength in her shoulders. No rash is appreciated. Laboratory evaluation reveals increased creatinine phosphokinase, positive antinuclear antibody, and positive anti-signal recognition particle. She is started on high-dose corticosteroids. (Polymyositis)
Introduction
  • Clinical definition
    • dermatomyositis is an autoimmune myopathy characterized by
      • symmetric proximal muscle weakness and rash
        • the clinical variant includes amyopathic dermatomyositis (dermatomyositis without myositis)
    • polymyositis is an autoimmune myopathy characterized by
      • symmetric proximal muscle weakness and no rash
  • Epidemiology
    • demographics
      • female > male
      • typically in adults 30-50 years of age
      • if in children, considered juvenile dermatomyositis
    • risk factors
      • drugs
      • physical exertion
  • Pathogenesis
    • dermatomyositis
      • an antibody-driven autoimmune disease characterized by perimysial inflammation and atrophy, resulting in muscle tissue damage
        • perimysium is closer to the skin and therefore has cutaneous manifestations – “dermato”
      • associated with CD4+ lymphocytes and complement activation
    • polymyositis
      • T-cell driven autoimmune disease characterized by endomysial inflammation
        • endomysium is farther from the skin and therefore has no cutaneous manifestations
      • associated with CD8+ lymphocytes
  • Associated conditions
    • interstitial lung disease
    • malignancy including
      • breast or ovarian cancer
      • prostate cancer
      • lung cancer
    • other connective tissue diseases
  • Prognosis
    • dermatomyositis
      • ↑ risk of malignancy (typically develops within 5 years of diagnosis)
Presentation
  • Symptoms
    • progressive weakness in hips and shoulders
    • dysphagia
    • dysphonia
      • laryngeal muscle weakness
  • Physical exam
    • dermatomyositis
      • characteristic cutaneous findings
        • a photosensitive pink rash of the neck and trunk
          • shawl or V-sign, as it often appears as sunburn with V-neck t-shirt
        • purple/lilac or red rash around eyes and on eyelids (heliotrope rash)  
          • can resemble a malar rash
        • raised violaceous, slightly scaly plaques, on bony prominences of the hands and elbows (Gottron papules) 
          • “mechanic’s hands” 
    • polymyositis and dermatomyositis
      • proximal muscle weakness in the shoulders and hips
        • difficulty combing hair
        • difficulty raising arms
        • difficulty rising from a chair
Studies
  • Labs
    • ↑ creatinine phosphokinase (CPK or CK)
    • ↑ creatine kinase-MB (CK-MB)
    • ↑ aldolase
    • ↑ lactate dehydrogenase (LDH)
    • autoantibodies
      • + antinuclear antibody (ANA)
      • + anti-Jo-1 (~20% of patients)
      • + anti-signal recognition particle (SRP) (~5% of patients)
        • usually associated with polymyositis
      • + anti-Mi-2 (<10% of adults)
        • usually associated with dermatomyositis
  • Muscle biopsy  
    • indication
      • diagnostic gold standard to differentiate between inflammatory and non-inflammatory myopathies
    • findings
      • degenerating muscle fibers and inflammatory infiltrates
      • dermatomyositis
        • perimysial inflammation
      • polymyositis
        • endomysial inflammation 
  • Making the diagnosis
    • based on clinical presentation and laboratory studies
Differential
  • Systemic lupus erythematosus
  • Localized scleroderma
  • Infectious myopathy
  • Myasthenia gravis
  • Inclusion body myositis 
    • presents with weakness and elevated CRP/CK
    • biopsy demonstrates endomysial inflammation with basophilic-rimmed vacuoles
Treatment
  • Management approach
    • both diseases are often treated initially with a course of steroids, followed by long-term immunosuppression
  • Conservative
    • sun protection
      • indication
        • for all patients with dermatomyositis
  • Medical
    • systemic steroids (high-dose) 
      • indications
        • for all patients with myositis as first-line therapy 
        • 2-4 weeks with subsequent taper
    • antimalarial
      • indications
        • for patients with primarily skin manifestations of dermatomyositis
        • drugs
          • hydroxychloroquine
    • non-steroidal immunosuppression
      • indications
        • for refractory disease
        • for prevention of recurrence after steroid taper
        • drugs
          • methotrexate
          • azathioprine
Complications
  • Cardiomyopathy
  • Macrophage activation syndrome
 

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Questions (6)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
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(M2.RH.4727) A 48-year-old Caucasian female presents to her primary care physician for evaluation of progressive weakness and shortness of breath. She has had progressive shortness of breath over the last year with an intermittent non-productive cough. In addition, she complains of difficulty raising her arms to brush her hair. Her temperature is 99.6°F (37.6°C), pulse is 80/min, blood pressure is 130/85 mmHg, respirations are 18/min, and oxygen saturation is 95% on room air. Neurologic exam shows 4/5 strength in the deltoid muscles bilaterally. Diffuse dry crackles are heard on lung auscultation. A faint erythematous rash is noted on the malar cheeks, periorbital areas, lateral proximal thighs, and the elbows. Which of the following tests is most likely to confirm the diagnosis? Review Topic

QID: 108589
1

Muscle biopsy

85%

(17/20)

2

CT scan

0%

(0/20)

3

Pulmonary function tests

0%

(0/20)

4

Serum ANA titer

5%

(1/20)

5

Skin biopsy

10%

(2/20)

M2

Select Answer to see Preferred Response

PREFERRED RESPONSE 1

(M3.RH.12) A 39-year-old woman comes into your office with multiple complaints of recent onset. She has been feeling fatigued and has started having leg and thigh pain bilaterally, along with weakness. In addition, she states that she recently started noticing some redness around her eyes along with a rash on her shoulders as shown in Figure A. Of note, she takes simvastatin for her hyperlipidemia, and took a short course of steroids recently for an allergic reaction. Her vitals are within normal limits. Her CK is 400 U/L, ESR is 70 mm/hr, and ferritin is 500 mcg/L. What is the most likely diagnosis? Review Topic

QID: 102766
FIGURES:
1

Inclusion body myositis

0%

(0/0)

2

Corticosteroid induced myopathy

0%

(0/0)

3

Statin induced myopathy

0%

(0/0)

4

Dermatomyositis

0%

(0/0)

5

Polymyositis

0%

(0/0)

M2

Select Answer to see Preferred Response

PREFERRED RESPONSE 4

(M3.RH.70) A 40-year-old woman presents to her primary care physician with complaints of worsening muscle aches and diffuse weakness over the past several months. She states that she now has difficulty climbing stairs and extending her neck. Ultimately, she became more concerned when she began having trouble swallowing and experienced shortness of breath last night which has resolved. Her temperature is 98.5°F (36.9°C), blood pressure is 120/84 mmHg, pulse is 70/min, respirations are 12/min, and oxygen saturation is 98% on room air. Physical exam is notable for 2/5 strength of the proximal muscles of the upper and lower extremities. Dermatologic, cardiac, and pulmonary exam are unremarkable. The patient is tolerating oral secretions and has no difficulty swallowing or protecting her airway currently. Laboratory studies are notable for an elevated CRP and aldolase. Which of the following is the most appropriate treatment for this patient? Review Topic

QID: 103011
1

Intravenous immunoglobulin

0%

(0/3)

2

Methotrexate

0%

(0/3)

3

Naproxen

100%

(3/3)

4

Neostigmine

0%

(0/3)

5

Prednisone

0%

(0/3)

M2

Select Answer to see Preferred Response

PREFERRED RESPONSE 5
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