P0421 - A Deadly Misdiagnosis: A Case of a Rare Tick-Borne Illness associated with Reversible Splenial Lesion Syndrome

Rocky Mountain Spotted Fever (RMSF) was last reported in 2006 in Michigan, however given the increased morbidity and mortality rate associated with a late diagnosis, it is an important diagnostic consideration.
A 10-year-old female presented with 4 day history of fever, headache and rash to the Emergency Room after visiting Northern Michigan. On presentation, the patient was febrile to 39.3 C, tachycardic to 116 beats/min, and normotensive. Physical examination revealed morbilliform rash around neck, back, and trunk. Upon admission to the floor, the patient had a transient 5-minute episode of hallucination. She was alert, but not oriented to time or place. She was empirically started on Acyclovir, Ceftriaxone, and Doxycycline at meningitic dosing after obtaining a Lumbar Puncture, which was largely within normal limits. Brain MRI revealed an abnormal focal diffusion restriction within the splenium of the corpus callosum as well as a few tiny nonspecific T2 and FLAIR hyperintensities in the left frontal deep and subcortical white matter. Various serologies were drawn, but of note, the patient’s Rickettsia Rickettsii IgG antibody was positive with a titer of 1:256 and IgM antibody was <1:64. Overall, the patient was hospitalized for 8 days and her clinical status improved steadily. Repeat imaging 8 weeks later revealed resolution of the focal diffusion restriction in the splenium and a few nonspecific foci of FLAIR signal scattered in the subcortical white matter, that were better visualized in comparison to the previous MRI. The finding of abnormal focal diffusion restriction within the splenium of the corpus callosum that resolved with treatment suggests Reversible Splenial Lesion Syndrome (RESLES). RESLES is a rare and non-specific radiologic syndrome that is associated with hypoglycemia, hyponatremia, epilepsy, influenza, and HIV. RESLES has not been described in association with RMSF.
Overall, RMSF is rarely reported in Michigan and clinicians should consider it in the differential diagnosis for patients with morbilliform or petechial skin rash, CNS symptoms and history of exposure. Prior to the determination of effective antibiotic treatment, 25% to 30% of patients with RMSF died. In a recent study, 3% of children with RMSF died and 15% of survivors had significant neurological deficits at the time of hospital discharge. The mortality risk also increases by more than 3-fold where therapy is delayed beyond the fifth day of illness. Our case reiterates the importance of early diagnosis and treatment as well as highlights the use of MRI as a viable aid in diagnosis of children with suspected RMSF. Lastly, RESLES in the setting of RMSF as described in our case, is a particularly unique addition to the literature.