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InFocus

Tick Paralysis

Rare and Easily Overlooked

Roberts, James R. MD

doi: 10.1097/01.EEM.0000554845.01379.e9
InFocus

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Most emergency clinicians will never see a case of tick paralysis in their entire career. Few even look for a tick in patients with neurological conditions, but tick paralysis can lead to significant morbidity and death if missed. The treatment of tick paralysis is simple—merely remove the tick. This condition is so rare, however, it is rarely suspected and even more rarely investigated while other incorrectly diagnosed conditions are treated.

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Tick Paralysis

Pecina CA

Semin Neurol

2012:32(5):513

This is a short report in a journal not read by emergency clinicians. The author described a characteristic case, a 49-year-old man who presented to the ED with complaints of difficulty walking. He was noted to have an ataxic gate. The patient developed flaccid ascending paralysis over the next few hours. It first affected the lower extremities with areflexia, and the same conditions quickly progressed to the upper extremities. Shortly after, he was noted to have significant dysarthria, drooling, and facial weakness. His breathing became labored, and he was placed on a ventilator in the intensive care unit. An MRI and lumbar puncture demonstrated no abnormalities, but he was diagnosed with Guillain-Barré syndrome and started on IVIG.

Tick paralysis was not suspected although his history included a hiking trip to Colorado two days before presentation. Fortunately, while repositioning the patient in the ICU, a nurse discovered a tick on the patient's scalp. It was removed, and the patient was tolerating the positive airway pressure on the ventilator within hours, and the next day he was able to breathe on his own. He was shortly moving all his extremities, and was discharged from the hospital with no neurological deficits.

Most cases of tick paralysis have been reported from Australia and North America, and a number of ticks have been reported as a causative species. It is postulated that paralysis is caused by salivary neurotoxins secreted by the female tick while feeding on the blood of the individual. The exact mechanism of the toxin and how it produces paralysis is not known. Some suggest that the secreted toxin interferes with the presynaptic release of acetylcholine and interferes with neural transmission to motor nerves.

Most cases of tick paralysis are reported in children and occur in the spring and summer. The long hair of girls is classic place for a tick to hide. Ticks are usually found on the scalp, but they can be in the neck, axilla, groin, buttocks, or behind the ear. They are rarely visible in these spots, do not cause local symptoms, and are unknown to the patient.

Lower extremity symptoms usually begin within two to six days of tick attachment, and if the tick remains attached, weakness ascends to the upper extremities. This occurs over a matter of hours and is quickly followed by a cranial nerve involvement such as drooling, dysphagia, dysphonia, and facial weakness. Deep tender reflexes are diminished or absent. Sensory function is preserved. If not recognized and treated, the clinical condition progresses to respiratory paralysis and death.

Before the neurological symptoms present, the patient may occasionally have a prodrome of restlessness, irritability, fatigue, diffuse paresthesias, and myalgia. Fever is absent. Basis laboratory tests are normal, including CSF studies. EMG abnormalities have also been described.

Tick paralysis can be misdiagnosed as Guillain-Barré syndrome, and the Miller Fisher variant involves the cranial nerves. The difference between tick paralysis and Guillain-Barré, aside from the normal CSF findings with tick paralysis, is that the weakness progresses much more quickly than generally seen with Guillain-Barré, which has an elevated protein concentration in the CSF not seen with tick paralysis.

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Fortunately, patients experience a full neurological recovery with no lasting deficits if the tick is removed. Full neurological recovery is rather rapid, and symptoms fully abate within a day or two.

Other missed diagnoses of tick paralysis include cerebellitis, botulism, transverse myelitis, spinal cord ischemia or tumor, myasthenia gravis, and paralytic hysteria. The key to suspecting the diagnosis is recognizing the rapidly evolving neurological symptoms.

Comment: I have never seen a case of tick paralysis, but I have seen a number of patients who presented in the ED after they discovered that a tick had attached itself. Quick removal probably accounts for the rarity of the syndrome.

More than 40 species of ticks can cause the syndrome, including the dog and Rocky Mountain wood ticks, but this is certainly a rare condition. Only about one case a year is reported in Colorado. Children are more commonly involved, likely because their small body size can concentrate the toxin.

The differentiation between Guillain-Barré syndrome and tick paralysis is the rapidity with which the paralysis ascends. A spinal tap is often performed in the ED if Guillain-Barré is suspected, and the classic finding is an elevated protein level with an otherwise normal LP and normal lab tests. Failure to find a cause of unusual neurological symptoms can prompt a diagnosis of hysterical paralysis. It certainly would be a potential disaster to make a psychiatric diagnosis in a patient with ataxia and and the findings of ascending paralysis.

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You may never see a case of tick paralysis, but it's a good idea to keep this in your differential diagnosis when evaluating patients with rapidly ascending paralysis and ataxic gait. Sensation will be normal because this involves a motor toxin, but patients may complain of widespread numbness and tingling.

Removing the tick is best accomplished by grasping the tick as closely as possible to the attachment site using forceps or tweezers with steady traction to avoid breaking the body from the head and mouth parts. (See photo and caption.) Squeezing the body just releases more neurotoxins. Whether this would affect the course is unknown, but it's better to be safe and remove the tick with an instrument. A search for other ticks is also essential. (See box.)

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Dr. Robertsis a professor of emergency medicine and toxicology at the Drexel University College of Medicine in Philadelphia. Read the Procedural Pause, a blog by Dr. Roberts and his daughter, Martha Roberts, ACNP, PNP, athttp://bit.ly/EMN-ProceduralPause, and read his past columns athttp://bit.ly/EMN-InFocus.

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