Imaging appearance of ticks in tick paralysis
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LETTER TO THE EDITOR
Imaging appearance of ticks in tick paralysis Mark R. Halverson 1
&
Micheline Lagacé 1 & Anna E. Smyth 1 & Ziad Abu Sharar 1 & Michael A. Sargent 1
Received: 28 July 2020 / Revised: 28 July 2020 / Accepted: 9 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Dear Editors, Just over a century ago, physicians John Todd [1] and Seymour Hadwen [2], in British Columbia, Canada, began research into local cases of acute ascending paralysis in children that seemed related to ticks most commonly found in the Pacific Northwest region of North America. Through surveys of regional physicians and animal experiments, they discovered that Dermacentor ticks caused acute ascending paralysis in children, a condition that could be fatal but that was easily treated by tick removal. Further research identified the toxin produced in the tick salivary glands that reduces neurotransmitter release at the neuromuscular junction and decreases peripheral nerve transmission [3]. This toxic effect can mimic Guillain–Barré syndrome clinically but does not lead to brain or spinal cord or nerve root imaging findings on CT or MRI. A patient could potentially be diagnosed with Guillain–Barré syndrome mistakenly and given ineffective treatment if the tick is not found and removed. The presence of the tick is usually discovered by clinical physical examination, but particularly when the tick is hidden by hair on the scalp, it can be difficult to detect. Radiologists can help make the diagnosis of tick paralysis if they are aware of the need to include the scalp in their search pattern in cases of ascending paralysis, and if they recognize the imaging appearance of the tick itself.
* Mark R. Halverson [email protected] 1
Radiology Department, British Columbia Children’s Hospital, University of British Columbia, 4480 Oak St., Vancouver, BC V6H 3N1, Canada
To our knowledge, only one case of an MRI showing the presence of a tick exists in the literature [4]. On those images 15 years ago, the tick is quite difficult to visualize and has very little signal intensity. Continued advances in imaging technology might allow better visualization now, and the degree of blood engorgement shown by the tick might influence its imaging appearance. Recently, at British Columbia Children’s Hospital, a 2-year-old previously healthy girl awoke with an unsteady wide-based gait. Clinical observations included absent lower-extremity reflexes, diminished upperextremity reflexes, mild generalized hypotonia and weakness. The next day she developed bulbar symptoms including ophthalmoplegia, dysarthria and dysphagia with progressive extremity and axial weakness. Cerebrospinal fluid analysis as well as brain and spine imaging studies were normal. As the neurology team prepared to treat the girl for a Miller–Fisher variant of Guillain–Barré syndrome, the girl’s mother found a tick on her left occipital scalp that was identified as Dermacentor andersoni. The girl experienced slow progression of symptoms for 16 h after t
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