Case
A healthy 6-year-old boy who lives on a farm in the Fraser Valley in British Columbia presented to a community hospital with new onset of ataxia. After waking that morning, he complained of leg weakness with accompanying paresthesia in his hands and feet. His past medical history was unremarkable and he did not have any preceding illness. There was no relevant travel history.
On examination he had a marked unsteady, wide, ataxic gait. He demonstrated slight asymmetrical weakness of his distal lower limbs with ankle plantarflexion strength graded as a 4 out of 5 on the left and 5 out of 5 on the right. Strength at the knee and hip was equal and 5 out of 5 bilaterally. His tone was mildly decreased. His ankle and patellar reflexes were absent. Cerebellar examination demonstrated dysdiadochokinesia and dysmetria that was more pronounced on the left side. He had bilateral horizontal nystagmus. Sensation to touch was decreased on the plantar surfaces of both feet. Although he complained of paresthesia in his hands, he did not have decreased sensation in his upper limbs. Findings of the remainder of his systemic examination were unremarkable. Initial laboratory investigation findings including white blood cell count and C-reactive protein levels, extended electrolyte levels, kidney function, urine toxicology, and urinalysis were normal. Findings from blood and urine cultures were negative. Neuroimaging was considered important before performing a lumbar puncture.
The differential diagnosis included Guillain-Barré Syndrome (GBS) owing to the presentation of an acute ascending paralysis, albeit slightly asymmetrical. Factors against this diagnosis were the ataxia and the cerebellar signs. Ingestion of a toxic substance, acute cerebellar ataxia, and a space-occupying lesion were also considered. As our hospital is a level 1 community hospital, the pediatric neurology team at BC Children’s Hospital in Vancouver was consulted. Immediate transfer to that hospital was recommended for further investigations (including neuroimaging) and management.
While awaiting transfer, the boy’s father raised a concern after he felt something in the child’s hair. An examination revealed a large engorged tick attached to the child’s scalp. The tick was removed using forceps. It was alive, with intact mouth pieces, and it was secured for laboratory analysis. No other attached ticks were found in a head-to-toe examination. The patient was then transferred to BC Children’s Hospital, after which his symptoms resolved within 24 hours. The provincial laboratory identified the tick as a female Dermacentor andersoni, commonly known as the Rocky Mountain wood tick.
Discussion
Tick paralysis is a rare but readily treatable neurologic syndrome. Left untreated it can be fatal. Unfortunately, it is often misdiagnosed, resulting in unnecessary interventions.
Tick paralysis occurs in regions coinciding with the habitats of tick species capable of secreting neurotoxins.1 The most common species affecting western North America is D andersoni, whose habitats include Alberta and British Columbia in Canada and the Pacific Northwest and Rocky Mountain areas of the United States.1-3 Incidence data for tick paralysis are limited. One study in Washington State identified 33 reported cases of tick paralysis between 1946 and 1996, of which 82% involved children younger than 8 years. Another study from British Columbia identified 24 cases between 1993 and 2016, of which 46% involved children younger than 10 years and most occurred in the Kootenay and Interior regions.4 However, in today’s environment of rapid travel, the condition can present outside these regions.5 Since gravid female ticks produce the causative neurotoxin, cases are typically seen in the warmer spring and summer months that coincide with tick breeding.1-3
The neurotoxin is produced and concentrated in the tick’s salivary glands and injected into its host while feeding.1,2 It is thought to target peripheral efferent motor neurons at the neuromuscular junction by inhibiting acetylcholine release.2,5
Tick paralysis has a higher occurrence in children, as their exposure to the neurotoxin on a milligram per kilogram basis is greater than in adults.2 The most common sites for tick bites are the scalp, neck, ear, nose, and groin.1-3 A capable tick will usually have been attached for 2 to 6 days before the concentration of the neurotoxin is high enough to cause symptoms.5
The presentation occurs in 2 distinct phases.1 The first prodromal phase is nonspecific and symptoms may include lethargy, weakness, paresthesia, myalgia, and a low-grade fever.1-3 As feeding continues the neurotoxic phase follows, resulting in an acute ataxia with diminished or absent deep-tendon reflexes.1,3 This rapidly progresses to an ascending flaccid paralysis with weakness ascending from legs to arms over a 24- to 48-hour period.2 This rapid progression is a key feature distinguishing tick paralysis from other causes of acute ascending paralysis. Sensorium is preserved, although nonspecific paresthesia can occur.2 Continued progression may result in cranial nerve involvement including facial nerve palsy, ophthalmoplegia, drooling, dysphagia, and dysphonia.1,2 Ultimately, diaphragmatic involvement results in respiratory compromise.2 This patient’s presentation was consistent with the early neurotoxic phase of tick paralysis.
Tick paralysis must be considered in the differential diagnosis for an acute ascending paralysis. Other differential considerations include GBS, poliomyelitis, acute spinal cord lesion, botulism, and acute cerebellar ataxia.1-3
The diagnosis of tick paralysis depends on a thorough head-to-toe search for an engorged, attached tick.2 Findings of investigations are typically unremarkable, with normal laboratory and cerebrospinal fluid (CSF) values.1,2 Nerve conduction study results are similar to those of patients with GBS, with reduced amplitude compound muscle action potentials, decreased nerve conduction velocity, and normal sensory nerve action potentials.1,3
The misdiagnosis of tick paralysis is common, most often as GBS.1-3 Both can present with similar prodromal symptoms, and both result in an ascending flaccid paralysis with absent reflexes.2 While GBS is a much more common cause of an acute ascending paralysis, it should be noted that the incidence of GBS in children (0.6 per 100 000) is far lower than in adults (2.7 per 100 000).6 Key differentiating features between GBS and tick paralysis include the following:
GBS evolves much more slowly than tick paralysis, with progression to maximal symptoms taking up to 4 weeks.2
Ataxia is not a feature of GBS.1
CSF studies typically feature elevated protein levels in GBS, but not in tick paralysis. There are no other distinguishing laboratory investigation findings.1
Botulism results in a slowly progressive descending paralysis.2,3 Acute spinal cord lesions typically result in upper motor neuron signs of hyperreflexia, spasticity, and clonus below the level of the lesion.7 Poliomyelitis is extremely uncommon following effective immunization programs, but it can still occur with travel to endemic areas. Poliomyelitis presents with an asymmetric weakness, infectious symptoms, and abnormal CSF values.1-3 It is worth noting that Lyme disease, the better-known tick-borne disease, may also present with neurologic involvement including cranial nerve palsy (especially cranial nerve VII), radiculopathy, and lymphocytic meningitis.8
Conclusion
The only definitive treatment for tick paralysis involves the identification and immediate removal of an attached, engorged tick.1,2 This results in rapid neurologic improvement within hours and complete resolution by 36 hours.1,3
The recommended method of tick removal involves using tweezers or forceps to grasp the tick as closely to the skin’s surface as possible. Care should be taken not to grasp the tick with too much force to avoid squeezing more toxin into the patient.2,3 The tick is then removed by pulling perpendicularly to the skin surface with gentle, steady traction. The goal is to remove the tick with its mouth parts, including its salivary glands, intact.1,9 Once the tick is removed, the area should be cleaned with rubbing alcohol, an iodine scrub, or soap and water.9
Educating the public about ticks and the risks of tick-infested areas is the first step in preventing tick bites. A simple measure is to avoid exposure to ticks in places where they are known to live and breed, particularly in wooded areas.9 Recommendations include wearing loose-fitting clothing that covers the arms and legs and tucking shirts into pants and pants into socks.10 It is easier to spot ticks on light-coloured clothing.10 Full body checks for ticks should be done following potential exposure.9,10 Showering within 2 hours of exposure is also recommended. Repellents effective against ticks include 20% to 30% DEET or icaridin repellent.9 There is insufficient evidence that soybean and citronella oil–based repellents protect against tick bites.10
Notes
Editor’s key points
▸ Tick paralysis is a rare cause of ascending paralysis. It is commonly misdiagnosed as Guillain-Barré Syndrome (GBS); however, GBS has a slower progression, lacks ataxia, and has elevated cerebrospinal fluid protein levels compared with tick paralysis. A diagnosis of GBS should not be made without first considering tick paralysis.
▸ Diagnosis involves a thorough head-to-toe search for attached ticks with particular attention paid to the patient’s scalp, neck, ears, nose, and groin.
▸ Tick removal results in rapid improvement within hours and complete resolution within 36 hours. The recommended method of removal involves using forceps or tweezers, grasping the tick close to the skin, and pulling with steady traction while avoiding leaving the tick’s mouth parts embedded in the skin.
▸ Prevention involves avoiding tick exposure, looking for attached ticks, and using appropriate clothing and repellents.
Points de repère du rédacteur
▸ La paralysie due à une piqûre de tique est une cause rare de paralysie ascendante. Elle est souvent prise à tort pour le syndrome de Guillain-Barré (SGB); cependant, le SGB progresse plus lentement, ne comporte pas d’ataxie et se distingue par des taux élevés de protéines dans le liquide céphalorachidien par rapport à ceux observés dans la paralysie due aux tiques. Il ne faudrait pas poser de diagnostic de SGB sans avoir envisagé d’abord une paralysie due aux tiques.
▸ Le diagnostic exige une recherche rigoureuse, de la tête aux pieds, pour repérer des tiques qui seraient fixées à la peau, en portant une attention particulière au cuir chevelu, au cou, aux oreilles, au nez et à l’aine du patient.
▸ Le retrait des tiques entraîne en quelques heures une amélioration rapide et une disparition complète en 36 heures. La méthode recommandée pour le retrait est d’utiliser des forceps ou des pinces à épiler, en saisissant la tique près de la peau et en tirant d’une traction constante tout en évitant de laisser dans la peau des parties buccales de la tique.
▸ Comme mesures de prévention, il faut éviter l’exposition aux tiques, procéder à un examen pour repérer des tiques fixées à la peau, porter des vêtements appropriés et utiliser des insectifuges.
Footnotes
Competing interests
None declared
This article has been peer reviewed.
Cet article a fait l’objet d’une révision par des pairs.
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