Pediatric Rocky Mountain Spotted Fever Workup

Updated: Apr 14, 2021
  • Author: Asif Noor, MD; Chief Editor: Russell W Steele, MD  more...
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Approach Considerations

Laboratory findings may be nonspecific in Rocky Mountain spotted fever (RMSF). On the complete blood cell count, the total leukocyte count may be normal, elevated, or decreased but usually shows a left shift.

Mild anemia and thrombocytopenia of less than 150 × 109/L (< 150 × 103/µL) occur in approximately one third of patients. Severe thrombocytopenia of less than 20 × 109/L (< 20 × 103/µL) occurs in approximately 10% of patients.

On a comprehensive metabolic panel, the following may be noted:

  • Hyponatremia (serum sodium < 130 mEq/L) in 20% of patients

  • The serum alanine aminotransferase level is usually increased

  • Serum albumin values may be low

  • The blood urea nitrogen (BUN) level is increased

Results of cerebrospinal fluid (CSF) analysis are generally normal. However, mild pleocytosis may be present, and approximately 50% of patients have a predominance of polymorphonuclear cells. An elevated CSF protein level may also be observed.

Serologic assays to detect anti–R rickettsii immunoglobulin G (IgG) antibodies are usually performed for definitive diagnosis. [10] Testing of acute-phase and convalescent-phase sera is recommended to demonstrate a 4-fold or higher increase in the titer.

Enzyme immunoassays (EIAs) and immunoglobulin M (IgM) antibody-capture immunoassays are new serologic tests that potentially allow for early diagnosis.

In research laboratories, isolation of rickettsiae from tissues or direct detection of rickettsiae in tissues by means of direct immunofluorescence is used to confirm the diagnosis. Polymerase chain reaction tests have been developed but are not widely available.


Imaging Studies

CT imaging is typically normal, whereas MRI seems more sensitive at revealing abnormalities. Published findings include diffuse edema, effacement of the sulci, arterial infarctions, prominent perivascular spaces, and enhancement of the meninges (ie typical findings of meningoencephalitis). In a case series of 3 pediatric cases of Rocky Mountain spotted fever (RMSF) with encephalitis, scattered nonenhancing punctate lesions were described throughout the cerebral white matter, visible on T2- and diffusion-weighted MRI. [11, 12, 13]