Polymyositis

Background

• Idiopathic inflammatory myopathy causing symmetric proximal muscle weakness, elevated CK, and characteristic EMG findings

Clinical Features

• Symmetrical proximal muscle weakness with insidious onset
• Generally painless (though 30% have myalgia)
• Difficulty with kneeling, climbing stairs, combing hair, or rising from a seated position
• Weak neck extensors causing difficulty of holding head up
• Associated arthralgias

Differential Diagnosis

Myalgia

• Infection:
  • Viral infection (e.g. Influenza)
  • Bacterial infection
  • Spirochete infection (E.g. Dengue fever; Trichinella)
• Drugs:
  • Statins
  • Bisphosphonates
  • Corticosteroids
  • Ciprofloxacin
  • Clofibrate
  • Colchicine
  • Chloroquine
  • Emetine
  • Aminocaproic acid
  • Zidovudine
  • Bretylium
  • Penicillamine
  • Drugs causing hypokalemia
• Metabolic disorders:
  • Vitamin D deficiency
  • Mitochondrial myopathy
  • Scurvy
  • Osteomalacia
• Fibromyalgia
• Endocrine:
  • Hypothyroidism
  • Hyperthyroidism
  • Cushing’s syndrome
  • Adrenal insufficiency
  • Hyperparathyroidism
• Polymyalgia rheumatica
• Rhabdomyolysis
• Myositis
  • Polymyositis
  • Dermatomyositis
  • Myositis (peds)
• Systemic lupus erythematosus
• Rheumatoid arthritis
• Inclusion body myositis
• Sarcoidosis
• Scleroderma
• Sjögren’s syndrome
• Psychiatric (e.g. somatic manifestations of depression)
• Domestic abuse
• Crush injury
• Lyme disease
• Ehlers-Danlos syndrome(hypermobility syndrome)
• HIV myopathy
• Hypophosphatemia
• Hypokalemia
• Hypothermia
• Prolonged immobility
• Strenuous exercise (overuse) or heat stroke
• Seizure
• Severe volume contraction
• Alcoholism
• Muscular dystrophy
  • Duchenne
  • Becker
  • Limb-girdle
  • Facioscapulohumeral
  • Myotonic dystrophy
  • Myotonia congenita
• Compartment syndrome; Muscle infarction
• Neuropathic
• Chronic fatigue syndrome
• Vasculitis
• Sarcocystosis
• Spinal stenosis
• Diabetic lumbosacral plexopathy

Weakness

• Neuromuscular weakness
  • Upper motor neuron:
    • CVA
    • Hemorrhagic stroke
    • Multiple sclerosis
    • Amyotrophic Lateral Sclerosis (ALS) (upper and lower motor neuron)
  • Lower motor neuron:
    • Spinal and bulbar muscular atrophy (Kennedy's syndrome)
  • Spinal cord disease:
    • Infection (Epidural abscess)
    • Infarction/ischemia
    • Trauma (Spinal Cord Syndromes)
    • Inflammation (Transverse Myelitis)
      • Acute flaccid myelitis
    • Degenerative (Spinal muscular atrophy)
    • Tumor
  • Peripheral nerve disease:
    • Guillain-Barre syndrome
    • Toxins (Ciguatera)
    • Tick paralysis
    • Diabetic peripheral neuropathy
  • Neuromuscular junction disease:
    • Myasthenia gravis crisis
    • Botulism
    • Organophosphate toxicity
    • Lambert-Eaton myasthenic syndrome
  • Muscle disease:
    • Rhabdomyolysis
    • Dermatomyositis
    • Polymyositis
    • Alcoholic myopathy
• Non-neuromuscular weakness
  • Can't miss diagnoses:
    • ACS
    • Arrhythmia/Syncope
    • Severe infection/Sepsis
    • Hypoglycemia
    • Periodic paralysis (electrolyte disturbance, K, Mg, Ca)
      • Hypokalemic periodic paralysis
      • Thyrotoxic periodic paralysis
    • Respiratory failure
  • Emergent Diagnoses:
    • Symptomatic Anemia
    • Severe dehydration
    • Hypothyroidism
    • Polypharmacy
    • Malignancy
    • Aortic disease - occlusion, stenosis, dissection
  • Other causes of weakness and paralysis
    • Acute intermittent porphyria (ascending weakness)

Evaluation

Workup

• CBC
• ESR
• CRP
• CK: Most sensitive muscle enzyme
• Urinalysis
• Consider:
  • LDH
  • AST/ALT
  • Aldolase
  • RF
  • ANA
  • Anti-Jo-1
  • Myositis antibody panel

Diagnosis

• Typically requires muscle biopsy

Management

• Prednisone 1mg/kg/day for 4-8 weeks until CK returns to reference range
  • Followed by prednisone taper
• Other treatments that rheum may prescribe:
  • Methotrexate as second line for poor response to corticosteroids
  • Other agents with less evidence: IVIG, TNF Inhibitors

Disposition

• Rheumatology or neurology consultation either in ED or as outpatient depending on severity of symptoms

See Also

• Weakness