- Published on
Emergency And Acute Medicine – Dermatomyositis And Polymyositis
Basic Description
Dermatomyositis and polymyositis are systemic inflammatory myopathies and represent the most common group of acquired, potentially treatable causes of skeletal muscle weakness. Both conditions are characterized by progressive, symmetrical muscle weakness developing over weeks to months. Respiratory insufficiency may occur due to respiratory muscle involvement, and aspiration pneumonia can result from weak cough, pharyngeal muscle dysfunction, and esophageal dysmotility. Cardiac involvement may include myocarditis, conduction abnormalities, cardiomyopathy, and congestive heart failure. Arthralgias commonly affect the hands, wrists, knees, and shoulders. Ocular muscles are spared, although facial weakness may appear in advanced disease.
Etiology And Pathophysiology
The exact cause is unknown, but autoimmune mechanisms are central. There is a female predominance, with an incidence of approximately 1 per 100,000. Associations include HLA-B8 and HLA-DR3. Polymyositis may be linked to viral, bacterial, or parasitic infections, and both conditions coexist with collagen vascular diseases in about 20% of cases. In dermatomyositis, humoral immune mechanisms cause microangiopathy leading to muscle ischemia. In polymyositis, T-cell–mediated cytotoxicity predominates, with CD8 T cells and macrophages destroying non-necrotic muscle fibers expressing class I MHC. Complement deposition is an early lesion, followed by inflammation, ischemia, microinfarction, necrosis, and muscle fiber destruction.
Pediatric Considerations
Dermatomyositis occurs in both children and adults, whereas polymyositis is rare in children. Juvenile dermatomyositis primarily affects skin and skeletal muscle and may include vasculitis, calcinosis cutis, and lipodystrophy. Coxsackievirus infection has been associated with the juvenile form.
Clinical Presentation
Polymyositis presents with muscle pain and proximal muscle weakness without rash. Dermatomyositis presents with characteristic skin findings in addition to muscle pain and weakness. Constitutional symptoms include weight loss, fever, anorexia, morning stiffness, myalgias, and arthralgias. Patients commonly report fatigue during routine activities such as brushing hair, climbing stairs, reaching overhead, or rising from a chair. Dysphagia, dyspnea, and cough may be present. Weakness primarily involves proximal limb and girdle muscles early and may progress distally later.
Physical Examination Findings
General findings include fatigue, fever, weight loss, dysphagia, and progressive symmetrical proximal muscle weakness. Dermatomyositis skin findings include heliotrope rash with eyelid edema, Gottron papules over extensor joint surfaces, a V-shaped or shawl rash over the back and shoulders, periungual telangiectasias with abnormal cuticles, and “mechanic’s hands” with hyperkeratotic fissuring of the fingers.
Essential Emergency Assessment
Assessment should prioritize airway protection and evaluation for aspiration, respiratory compromise, and cardiac involvement.
Diagnostic Evaluation
Serum muscle enzymes are typically elevated, especially creatine phosphokinase, with possible elevation of aldolase. Diagnostic criteria include symmetrical proximal muscle weakness, elevated muscle enzymes, electromyographic evidence of myopathy, and muscle biopsy demonstrating inflammatory changes, with characteristic rash required for dermatomyositis. Newer criteria incorporate autoantibodies such as anti–Jo-1, anti–SRP, and anti–Mi-2. Chest radiography may show interstitial lung disease, aspiration pneumonia, or cardiomyopathy. EMG supports but does not confirm diagnosis. MRI is increasingly used to localize inflamed muscle for biopsy. Muscle biopsy remains definitive, showing endomysial inflammation in polymyositis and perivascular inflammation with B-cell predominance in dermatomyositis. Pulmonary function testing helps monitor interstitial lung disease.
Differential Diagnosis
Consider collagen vascular diseases, muscular dystrophies, spinal muscular atrophy, myasthenia gravis, amyotrophic lateral sclerosis, poliomyelitis, Guillain–Barré syndrome, endocrine disorders, Cushing syndrome, drug-induced myopathies, infections, electrolyte abnormalities, vasculitis, paraneoplastic syndromes, and hypereosinophilic myalgia.
Emergency Management
Initial care focuses on airway, breathing, and circulation, with head-of-bed elevation and early airway protection if needed. Mechanical ventilation may be required in severe respiratory weakness. Nasogastric suction can reduce aspiration risk. High-dose corticosteroids are the cornerstone of therapy to suppress inflammation and improve strength, avoiding agents known to cause steroid-induced myopathy. Treatment response should be judged by clinical improvement rather than enzyme levels alone. Immunosuppressive agents such as methotrexate or azathioprine may be added if steroid response is inadequate. Other therapies including IVIG, plasmapheresis, or cyclosporine are used selectively under specialist guidance.
Medication Therapy
First-line therapy is prednisone 60 mg daily orally, or weight-based dosing in children, with intravenous methylprednisolone pulses for severe disease. Second-line agents include methotrexate, azathioprine, IVIG, plasmapheresis, or cyclosporine as determined by rheumatology.
Disposition And Follow-Up
Admission is indicated for respiratory insufficiency, aspiration pneumonia, profound weakness, ineffective cough, pharyngeal dysfunction, or congestive heart failure. Stable patients without aspiration risk who can tolerate oral therapy may be managed as outpatients. Early rheumatology consultation is recommended. Because dermatomyositis carries an increased malignancy risk, ongoing cancer surveillance with regular examinations and screening studies is advised.
Key Clinical Insights
Diagnosis is primarily clinical and supported by laboratory testing and biopsy. Most patients improve with treatment, many achieving sustained functional recovery, though residual weakness may persist in up to one-third. Relapses can occur at any time despite prior successful therapy.
Basic Description
Dermatomyositis and polymyositis are systemic inflammatory myopathies and represent the most common group of acquired, potentially treatable causes of skeletal muscle weakness. Both conditions are characterized by progressive, symmetrical muscle weakness developing over weeks to months. Respiratory insufficiency may occur due to respiratory muscle involvement, and aspiration pneumonia can result from weak cough, pharyngeal muscle dysfunction, and esophageal dysmotility. Cardiac involvement may include myocarditis, conduction abnormalities, cardiomyopathy, and congestive heart failure. Arthralgias commonly affect the hands, wrists, knees, and shoulders. Ocular muscles are spared, although facial weakness may appear in advanced disease.
Etiology And Pathophysiology
The exact cause is unknown, but autoimmune mechanisms are central. There is a female predominance, with an incidence of approximately 1 per 100,000. Associations include HLA-B8 and HLA-DR3. Polymyositis may be linked to viral, bacterial, or parasitic infections, and both conditions coexist with collagen vascular diseases in about 20% of cases. In dermatomyositis, humoral immune mechanisms cause microangiopathy leading to muscle ischemia. In polymyositis, T-cell–mediated cytotoxicity predominates, with CD8 T cells and macrophages destroying non-necrotic muscle fibers expressing class I MHC. Complement deposition is an early lesion, followed by inflammation, ischemia, microinfarction, necrosis, and muscle fiber destruction.
Pediatric Considerations
Dermatomyositis occurs in both children and adults, whereas polymyositis is rare in children. Juvenile dermatomyositis primarily affects skin and skeletal muscle and may include vasculitis, calcinosis cutis, and lipodystrophy. Coxsackievirus infection has been associated with the juvenile form.
Clinical Presentation
Polymyositis presents with muscle pain and proximal muscle weakness without rash. Dermatomyositis presents with characteristic skin findings in addition to muscle pain and weakness. Constitutional symptoms include weight loss, fever, anorexia, morning stiffness, myalgias, and arthralgias. Patients commonly report fatigue during routine activities such as brushing hair, climbing stairs, reaching overhead, or rising from a chair. Dysphagia, dyspnea, and cough may be present. Weakness primarily involves proximal limb and girdle muscles early and may progress distally later.
Physical Examination Findings
General findings include fatigue, fever, weight loss, dysphagia, and progressive symmetrical proximal muscle weakness. Dermatomyositis skin findings include heliotrope rash with eyelid edema, Gottron papules over extensor joint surfaces, a V-shaped or shawl rash over the back and shoulders, periungual telangiectasias with abnormal cuticles, and “mechanic’s hands” with hyperkeratotic fissuring of the fingers.
Essential Emergency Assessment
Assessment should prioritize airway protection and evaluation for aspiration, respiratory compromise, and cardiac involvement.
Diagnostic Evaluation
Serum muscle enzymes are typically elevated, especially creatine phosphokinase, with possible elevation of aldolase. Diagnostic criteria include symmetrical proximal muscle weakness, elevated muscle enzymes, electromyographic evidence of myopathy, and muscle biopsy demonstrating inflammatory changes, with characteristic rash required for dermatomyositis. Newer criteria incorporate autoantibodies such as anti–Jo-1, anti–SRP, and anti–Mi-2. Chest radiography may show interstitial lung disease, aspiration pneumonia, or cardiomyopathy. EMG supports but does not confirm diagnosis. MRI is increasingly used to localize inflamed muscle for biopsy. Muscle biopsy remains definitive, showing endomysial inflammation in polymyositis and perivascular inflammation with B-cell predominance in dermatomyositis. Pulmonary function testing helps monitor interstitial lung disease.
Differential Diagnosis
Consider collagen vascular diseases, muscular dystrophies, spinal muscular atrophy, myasthenia gravis, amyotrophic lateral sclerosis, poliomyelitis, Guillain–Barré syndrome, endocrine disorders, Cushing syndrome, drug-induced myopathies, infections, electrolyte abnormalities, vasculitis, paraneoplastic syndromes, and hypereosinophilic myalgia.
Emergency Management
Initial care focuses on airway, breathing, and circulation, with head-of-bed elevation and early airway protection if needed. Mechanical ventilation may be required in severe respiratory weakness. Nasogastric suction can reduce aspiration risk. High-dose corticosteroids are the cornerstone of therapy to suppress inflammation and improve strength, avoiding agents known to cause steroid-induced myopathy. Treatment response should be judged by clinical improvement rather than enzyme levels alone. Immunosuppressive agents such as methotrexate or azathioprine may be added if steroid response is inadequate. Other therapies including IVIG, plasmapheresis, or cyclosporine are used selectively under specialist guidance.
Medication Therapy
First-line therapy is prednisone 60 mg daily orally, or weight-based dosing in children, with intravenous methylprednisolone pulses for severe disease. Second-line agents include methotrexate, azathioprine, IVIG, plasmapheresis, or cyclosporine as determined by rheumatology.
Disposition And Follow-Up
Admission is indicated for respiratory insufficiency, aspiration pneumonia, profound weakness, ineffective cough, pharyngeal dysfunction, or congestive heart failure. Stable patients without aspiration risk who can tolerate oral therapy may be managed as outpatients. Early rheumatology consultation is recommended. Because dermatomyositis carries an increased malignancy risk, ongoing cancer surveillance with regular examinations and screening studies is advised.
Key Clinical Insights
Diagnosis is primarily clinical and supported by laboratory testing and biopsy. Most patients improve with treatment, many achieving sustained functional recovery, though residual weakness may persist in up to one-third. Relapses can occur at any time despite prior successful therapy.
0 Comments
