Dermatomyositis/Polymyositis, Emergency Medicine

Basics

Description

Dermatomyositis (DM) and polymyositis (PM) are systemic inflammatory myopathies, which represent the largest group of acquired and potentially treatable causes of skeletal muscle weakness
Patients experience a marked progression of muscle weakness over weeks to months
Can lead to respiratory insufficiency from respiratory muscle weakness
Aspiration pneumonia can occur owing to a weak cough mechanism, pharyngeal muscle dysfunction, and esophageal dysmotility
Cardiac manifestations include myocarditis, conduction defects, cardiomyopathy, and congestive heart failure (CHF)
Arthralgias of the hands, wrists, knees, and shoulders
Ocular muscles are not involved but facial muscle weakness may be seen in advanced cases

Etiology

The exact cause is unknown, although autoimmune mechanisms are thought to be largely responsible
Incidence ~1:100,000 with a female preponderance
Association with HLA-B8 and HLA-DR3
There may be an association between PM and certain viral, bacterial, and parasitic infections
DM/PM occurs with collagen vascular disease about 20% of the time
In DM, humoral immune mechanisms are implicated, resulting in a microangiopathy and muscle ischemia
In PM, a mechanism of T-cell-mediated cytotoxicity is posited. CD8 T cells, along with macrophages surround and destroy healthy, non-necrotic muscle fibers that aberrantly express class I major histocompatibility complex (MHC) molecules
Deposition of complement is the earliest and most specific lesion, followed by inflammation, ischemia, microinfarcts, necrosis, and destruction of the muscle fibers

Although DM is seen in both children and adults, PM is rare in children
Similar to adult DM, juvenile DM (JDM) primarily affects the skin and skeletal muscles
Juvenile form may include vasculitis, ectopic calcifications (calcinosis cutis), and lipodystrophy
The juvenile form may be associated with coxsackievirus

Diagnosis

Signs and Symptoms

History

PM is distinguished from DM by the absence of rash
Patients with PM present with muscle pain and proximal muscle weakness
DM presents with skin rash, muscle pain, and weakness
Constitutional symptoms include weight loss, fever, anorexia, morning stiffness, myalgias, and arthralgias
Patients often note fatigue doing customary tasks:
- Brushing hair, climbing stairs, reaching above the head, rising from a chair
- May also complain of dysphagia, dyspnea, and cough
Progressive weakness of the proximal limb and girdle muscles is seen early; distal muscle weakness can occur late in the disease

Physical Exam

General:
- Fatigue
- Fever
- Weight loss
Dysphagia
Progressive muscle weakness:
- Involves proximal muscles primarily
- Symmetrical
Skin findings of DM:
- Skin rash occurs with or precedes muscle weakness
- Heliotrope rash (lilac discoloration) on the upper eyelids associated with edema
- Gottron sign: Violaceous or erythematous papules over the extensor surfaces of the joints, particularly knuckles, knees, and elbows
- Shawl sign: A V-shaped erythematous rash occurring on the back and shoulders
- Periungual telangiectasias: Nail-bed capillary changes that include thickened irregular and distorted cuticles
- "Machinist hands": Darkened horizontal lines across the lateral and palmar aspects of the fingers

Essential Workup

Assess airway and breathing for any signs of aspiration or compromise
Assess for any signs of cardiac involvement and complications

Diagnosis Tests & Interpretation

Lab

Serum muscle enzymes:
- Creatine phosphokinase (CPK) is elevated, other muscle enzymes such as aldolase, can also be elevated
Diagnostic criteria established in 1975 by Bohan and Peter:
- Symmetric proximal muscle weakness with dysphagia and respiratory muscle weakness
- Elevation of serum muscle enzymes
- Electromyographic features of myopathy
- Muscle biopsy showing features of inflammatory myopathy
- Confidence limits for diagnosis (typical rash must be seen for diagnosis of DM):
  - Definite diagnosis: 3 or 4 criteria
  - Probable diagnosis: 2 criteria
  - Possible diagnosis: 1 criterion
Newer diagnostic criteria using autoantibody profiles (Anti-Jo-1, Anti-SRP, Anti-Mi-2) or immunohistologic characterization may prove to be more specific for diagnosis of specific disease subgroups

Imaging

Chest radiograph may show interstitial lung disease, evidence of aspiration pneumonia, CHF, or cardiomyopathy
EMG studies show myopathic potentials that may support the diagnosis but are not specific for DM/PM
Increasing role for MRI in determining regions of inflammation best suited for biopsy

Diagnostic Procedures/Surgery

Muscle biopsy is the definitive test:
- In PM, inflammatory infiltrates are often endomysial, although they may be perivascular
- In DM, inflammatory infiltrates are mostly perivascular and include a high percentage of B cells
Renal biopsies of patients may show focal proliferative glomerulonephritis
Pulmonary function tests are useful in following the progression of interstitial lung disease

Differential Diagnosis

Collagen vascular diseases
Muscular dystrophies
Spinal muscular atrophy
Myasthenia gravis
Amyotrophic lateral sclerosis
Poliomyelitis
Guillain-Barr İ syndrome
Hypothyroidism
Hyperthyroidism
Cushing syndrome
Drug-induced:
- Colchicine
- Zidovudine (AZT)
- Penicillamine
- Ipecac
- Ethanol
- Chloroquine
- Corticosteroids
Infection:
- Toxoplasmosis
- Trichinosis
- Coxsackievirus
- HIV, influenza
- Epstein-Barr virus
Electrolyte disturbances:
- Hypokalemia
- Hypercalcemia
- Hypomagnesemia
Vasculitis
Paraneoplastic neuromyopathy
Hypereosinophilic myalgia syndrome

Treatment

Pre-Hospital

Assess ABCs
Transport with elevation of head of bed

Initial Stabilization/Therapy

Intubation and mechanical ventilation as required
Nasogastric (NG) suction to prevent aspiration
Pneumothorax has been described as a rare occurrence in childhood DM

Ed Treatment/Procedures

Elevate head of the bed to prevent aspiration
Begin high-dose corticosteroids to suppress inflammation and improve muscle weakness
Avoid triamcinolone and dexamethasone because they may cause a drug-associated myopathy
Efficacy of prednisone determined by objective increase in muscle strength, not change in CK levels
Some clinicians start glucocorticoid sparing immunosuppressive medications at onset, others reserve these agents for failure to respond to corticosteroids
Azathioprine and methotrexate are used with limitations based on side-effect profiles
Cyclosporine and monoclonal antibody therapies have been used but with limited success
Do not base treatment decisions solely upon CPK level

Medication

First Line

Prednisone: 60 mg/d PO (peds: 1-2 mg/kg/d PO) (in severe illness consider methylprednisolone pulse 1,000 mg/d for 3 days):
- Length of treatment and taper individualized to clinical response and normalization of CK

Second Line

Methotrexate: 15-25 mg PO per week (peds: 15 mg/m2/wk PO not >25 mg)
Azathioprine: Start at 50 mg/d then in 2 wk, increase by 50 mg until a dose of 1.5 mg/kg/d.
- After 3 mo, may increase dose to 2.5 mg/kg/d if tolerated
Intravenous immunoglobulin (IVIG), plasmapheresis, and cyclosporine are also used by some rheumatologists

Follow-Up

Disposition

Admission Criteria

Respiratory insufficiency
Aspiration pneumonia
Profound muscle weakness
Weakened cough mechanisms
Pharyngeal dysfunction
CHF

Discharge Criteria

Well-appearing patients with no respiratory dysfunction and no risk for aspiration
Patients who can take oral corticosteroids and immunosuppressive agents as outpatients

Issues for Referral
Consultation with a rheumatologist should be made when the diagnosis is suspected for assistance with definitive diagnosis and further treatment.

Follow-Up Recommendations

Compared to the general population, the incidence of malignant conditions appears to be increased in patients with DM (but not in those with PM)
A complete annual physical exam with pelvic, breast, and rectal exams; urinalysis; CBC; blood chemistry tests; and a chest film are often recommended for cancer surveillance in patients with a history of DM

Pearls and Pitfalls

The diagnosis of an inflammatory myopathy is largely clinical supported by selected lab testing and muscle biopsy
Most patients improve with therapy, and many make a full functional recovery, which is often sustained with maintenance therapy
Up to 30% may be left with some residual muscle weakness
It is important to keep in mind that relapses may occur at any time despite successful response to therapy

Additional Reading

Amato AA, Barohn RJ. Evaluation and treatment of inflammatory myopathies. J Neurol Neurosurg Psychiatry. 2009;80:1060-1068.
Casciola-Rosen L, Mammen AL. Myositis autoantibodies. Curr Opin Rheumatol. 2012;24:602-608.
Gordon PA, Winer JB, Hoogendijk JE, et al. Immunosuppressant and immunomodulatory treatment for dermatomyositis and polymyositis. Cochrane Database Syst Rev. 2012;8:CD003643.
Longo DL, Kasper DL, Jameson JL, et al. Polymyositis, dermatomyositis, and inclusion body myositis: Introduction. In Harrisons Principles of Internal Medicine. 18th ed. New York, FY: McGraw-Hill; 2012:2103-2103.
Wedderburn LR, Rider LG. Juvenile dermatomyositis: New developments in pathogenesis, assessment and treatment. Best Pract Res Clin Rheumatol. 2009;23:665-678.

Codes

ICD9

710.3 Dermatomyositis
710.4 Polymyositis

ICD10

M33.20 Polymyositis, organ involvement unspecified
M33.90 Dermatopolymyositis, unspecified, organ involvement unspecified
M33.92 Dermatopolymyositis, unspecified with myopathy
M33.22 Polymyositis with myopathy
M33.21 Polymyositis with respiratory involvement
M33.29 Polymyositis with other organ involvement
M33.2 Polymyositis
M33.91 Dermatopolymyositis, unsp with respiratory involvement
M33.99 Dermatopolymyositis, unsp with other organ involvement
M33.9 Dermatopolymyositis, unspecified

SNOMED

396230008 Dermatomyositis (disorder)
31384009 Polymyositis (disorder)
238935002 Dermatomyositis sine myositis
196136009 Lung disease with polymyositis (disorder)
239899000 Polymyositis associated with autoimmune disease (disorder)

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