Lab case 162 – Interpretation

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A 9 year old boy is referred in by his GP with abnormal blood results on a background of a viral like illness.

His blood tests show:A mild Leucopaenia and Neutropaenia

very high Creatine Kinase, with normal Potassium and renal function

Most likely due to a viral myositis on clinical picture, however he tested Mycoplasma IgM positive and IgG negative. His CXR did not show evidence of pneumonia.

Influenza myositis

  • Elevated CK, mostly consisting of the MM (muscle) isoenzyme, as high as 500 times normal
  • Urine myoglobin – May be positive
  • Liver enzymes (aspartate aminotransferase [AST] and lactate dehydrogenase [LDH]) – May be elevated
  • Detection of virus with polymerase chain reaction (PCR) testing of nasopharyngeal specimens
  • Viral IgM and IgG titers

Coxsackie virus myositis

  • Rising coxsackievirus IgG antibody titers
  • Isolation methods for group B coxsackievirus – Include inoculation of cell cultures

Streptococcal myositis

  • Leukocytosis
  • Elevated muscle enzyme levels

Mycoplasma Myositis

  • Serology for IgM

Fungal myositis – Fungal stain and culture

Other Causes:

Pyomyositis

  • Leukocytosis
  • Elevated erythrocyte sedimentation rate (ESR)
  • Serum creatine kinase (CK) and aldolase usually normal
  • Blood culture results generally negative
  • Purulent material for Gram stain, anaerobic and aerobic cultures, antimicrobial sensitivity testingSerology:

Cysticercosis

Serology to aid diagnosis of:

HTLV-1 infection

Trypanosomiasis – ELISA (highly sensitive) or direct agglutination test

Trichinosis

  • A rising antibody titre is highly suggestive of the disease.
  • Eosinophilia is suggestive of the diagnosis.
  • Laboratory tests may also reveal leukocytosis, elevated immunoglobulin E, and increased muscle enzymes.

Toxoplasmosis

 

Cryptococcal myositis

  • Serology – Positive cryptococcal serum antigen
  • Muscle biopsy may reveal intracytoplasmic organisms
  • Alcian blue or mucicarmine stains may identify polysaccharide capsule

Lyme Disease (NOT IN AUSTRALIA)

  • If ELISA screening test result is positive, confirm with a Western blot test.Admit patient for observation and ensure:

Treatment and disposition:

  • adequate fluid intake and maintaining urine output
  • repeat CK ensure level decreases prior to discharge

CK levels rise within 12 hours of muscle injury, peak in 24-36 hours, and decrease at a rate of 30-40% per day.  The serum half-life of CK is approximately 36 hours. CK levels decline 3-5 days after resolution of muscle injury; failure of CK levels to decrease suggests ongoing muscle injury or development of a compartment syndrome. The peak CK level, especially when it is higher than 15,000 U/L, may be predictive of renal failure. 

Total CK elevation is a sensitive but nonspecific marker for rhabdomyolysis. CK levels 5 times the reference range suggest rhabdomyolysis, though CK levels in rhabdomyolysis are frequently as high as 100 times the reference range or even higher. Suspect early rhabdomyolysis in patients with serum CK levels in excess of 2-3 times the reference range and risk factors for rhabdomyolysis; initiate a full laboratory workup. Because the total CK may increase from the initial values, draw repeat total CK levels every 6-12 hours until a peak level is established.