A previously healthy 6-year-old girl is brought to the ED by her parents for overnight onset of “weakness” in her legs. She complained of minor tingling in her hands and feet the night before, but otherwise has been feeling well and had no recent illnesses. This morning, she was awoken from sleep by her parents, and immediately collapsed to the floor upon attempting to stand. She has no other complaints. Her past medical, family, and developmental histories are unremarkable. She lives in a rural, wooded area an hour outside of Birmingham, AL. Her vitals are appropriate for her age. Her neurologic exam is notable for symmetrically diminished strength and absent deep tendon reflexes in both legs. Coordination in her legs is notably impaired on heel-to-shin test, and when she is assisted to walk, she has an ataxic gait. Sensation is intact throughout. The rest of the patient’s neurologic and physical exam, labs, and imaging are unremarkable.
Before the patient is admitted, a second head-to-toe examination reveals an engorged tick attached to the girl’s scalp just above her R ear. The patient’s symptoms notably improve within hours of tick removal. She is admitted for observation, and by the next morning has complete resolution of her symptoms.
What is tick paralysis, when should it be suspected, and how is it diagnosed and treated?
Summary of Evidence/Recommendations:
While there are numerous case reports of tick paralysis, there is no high-quality evidence regarding its incidence, symptoms, or outcomes. This post will focus on cases of tick paralysis from the US.
Symptoms are caused by neurotoxins produced by females of over 40 species of ticks.(1)
Cases have been reported throughout the US, but predominantly in Western and Southern states.(2)
Ticks of the Dermacentor genus are the predominant culprits in the US, but have been attributed to a wide range of species, some featured in Figure 1 below.
Tick paralysis is rare, but incidence data are scarce. Notably, between 1946 and 1996 tick paralysis was a reportable condition in Washington State, and only 33 cases were documented in that time, with the 76% of cases occurring in females and 82% occurring in patients under the age of 83.
Notably, tick-paralysis is fully reversible with removal of the tick; therefore, the case-fatality rate is low (6-12%). Fatality is often associated with failure to diagnose and treat the illness, leading to subsequent respiratory failure.(3,4)
The mechanisms of action for toxins produced by ticks vary by species. Toxins from the Dermacentor genus have been noted to reduce conduction velocity and action potential amplitude of motor and sensory neurons in human patients,(5) while toxins from the Australian Ixodes holocyclus species have been shown to block Ca2+-dependent neurotransmitter release in animal models.(6)
Symptoms do not typically appear until the tick has been attached for several days.(7)
Ideally, tick paralysis is a purely clinical diagnosis
Classic history includes rapid onset (often <24-48hrs) of ascending weakness, ataxia, and parasthesias in the absence of other symptoms, most often occurring in children.(2,8)
Neurologic exam is often notable for motor weakness, preserved sensation, ataxia, hyporeflexia, predominantly in the lower extremities. Cranial nerves are most often intact.(2,8) Vitals and the rest of the physical exam will often be unremarkable.
Though laboratory studies, analysis of CSF, and imaging are not needed for diagnosis, these are most often unremarkable in the absence of respiratory failure.(2,8)
Definitive diagnosis requires identifying the tick, removing it from the patient, and monitoring them patient for improvement symptoms, which typically occur within hour of tick removal. Therefore, this is not a diagnosis of exclusion, but one that needs a high index of suspicion in the appropriate clinical context.
1. Gothe, R., Kunze, K. & Hoogstraal, H. Review Article: The Mechanisms of Pathogenicity in the Tick Paralyses. J Med Entomol 16, 357–369 (1979).
2. Diaz, J. H. A 60-year meta-analysis of tick paralysis in the United States: a predictable, preventable, and often misdiagnosed poisoning. J Med Toxicol 6, 15–21 (2010).
3. Dworkin, M. S., Shoemaker, P. C. & Anderson, D. E. Tick paralysis: 33 human cases in Washington State, 1946-1996. Clin. Infect. Dis. 29, 1435–1439 (1999).
4. Rose, I. A Review of Tick Paralysis. Can Med Assoc J 70, 175–176 (1954).
5. Felz, M. W., Smith, C. D. & Swift, T. R. A six-year-old girl with tick paralysis. N. Engl. J. Med. 342, 90–94 (2000).
6. Chand, K. K. et al. Tick holocyclotoxins trigger host paralysis by presynaptic inhibition. Sci Rep 6, 29446 (2016).
7. Simon, L. V., Hashmi, M. F. & McKinney, W. P. Tick Paralysis. in StatPearls (StatPearls Publishing, 2019).
8. Edlow, J. A. Tick paralysis. Curr Treat Options Neurol 12, 167–177 (2010).