Polymyositis

Background

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

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

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

Neuromuscular weakness
- Upper motor neuron:
  - CVA
  - Hemorrhagic stroke
  - Multiple sclerosis
  - Amyotrophic Lateral Sclerosis (ALS) (UMN & LMN)
- 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)
  - Degenerative (Spinal muscular atrophy)
  - Tumor
- Peripheral nerve disease:
  - Guillain-Barre syndrome
  - Toxins (Ciguatera)
  - Tick paralysis
  - Diabetic peripheral neuropathy
- NMJ disease:
- 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
- Other causes of weakness and paralysis
  - Acute intermittent porphyria (ascending weakness)

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

Rheumatology or neurology consultation either in ED or as outpatient depending on severity of symptoms
Very strongly associated with malignancy (~30%), especially:[1]
- Ovarian
- Lung
- Pancreatic
- Stomach
- Colorectal
- Lymphoma
- Bladder

Hill CL et al. Frequency of specific cancer types in dermatomyositis and polymyositis: a population-based study. Lancet. 2001 Jan 13;357(9250):96-100.

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