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We report severe tick paralysis in a child cared for at an academic medical center. Once the correct diagnosis had been established, intervention with the use of another common item — tweezers — resulted in rapid recovery.
Case Report
A previously healthy, six-year-old girl reported a tingling sensation in her fingers and six hours later began to stagger and fall. The next day, she was unable to walk without assistance. She was brought to the Medical College of Georgia 30 hours after the onset of symptoms. On initial examination, the child, who had long hair, was alert and afebrile, but had truncal instability and a wide-based, ataxic gait. She was unable to walk without support. Muscle strength was 4/5 in the legs and arms, proximally and distally. Dysmetria of the arms was noted on finger-to-nose testing. Muscle-stretch reflexes were diminished at the left knee but were normal elsewhere. The findings on tests of sensory-nerve and cranial-nerve function were normal, as was the rectal-sphincter tone. Chest radiographs and routine laboratory studies showed no abnormalities. Tests for toxic substances and a stool culture were negative. The initial differential diagnosis included acute cerebellar ataxia, cervical-cord compression, and the Guillain–Barré syndrome.
Magnetic resonance imaging studies of the head and neck showed no abnormalities. Analysis of a cerebrospinal fluid specimen revealed a protein level of 29 mg per deciliter, a glucose concentration of 71 mg per deciliter (3.9 mmol per liter), and a lymphocyte count of 2 per cubic millimeter. Gram's staining and a culture of cerebrospinal fluid were negative. Nerve-conduction studies performed 24 hours before the maximal weakness revealed that the distal latency of the ulnar nerve was prolonged, at 6.0 msec (normal value, <2.5) and that the amplitude of the muscle action potential of the peroneal nerve was moderately reduced (Table 1). There was no evidence of conduction block or late components.
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By 72 hours after the onset of illness, motor strength in the arms and legs had decreased to 2/5. Listlessness, slurred speech, and bilateral ptosis were observed. Because of the rapid deterioration in association with a presumed diagnosis of Guillain–Barré syndrome, preparation for femoral-vein access was initiated for emergency plasmapheresis.
During placement of the central catheter, an astute pediatric resident, aware that the Guillain–Barré syndrome can be confused with tick paralysis, carefully inspected the child's hair with a fine-toothed comb. To the surprise of the three pediatricians, the pediatric neurologist, and the pediatric intensivist who were caring for the child, an engorged tick, 15 mm in diameter, was embedded in the left parietal area of the scalp (Figure 1). It was identified as a female Dermacentor variabilis.4 The tick was promptly removed with tweezers, 78 hours after the onset of symptoms and 48 hours after admission to the hospital.
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Tick paralysis typically affects children, who present with paresthesias and leg weakness but without fever; they have difficulty walking and tend to fall. Adults are affected less frequently,5,6,7 presumably because the neurotoxin produced by the tick has a less pronounced effect because of their larger body mass. Within 24 to 48 hours, weakness in the legs ascends to the trunk musculature, and the patient can no longer sit or walk without assistance. Ascending paralysis, accompanied by hyporeflexia or areflexia, progresses to the arms, then to the bulbar structures involved in speech, swallowing, and facial expression, and eventually to the respiratory musculature. If the tick is not found and removed, respiratory weakness can lead to progressive hypoventilation, lethargy, coma, and death.
The clinical differentiation of tick paralysis from the Guillain–Barré syndrome and other causes of ascending paralysis is crucial because the therapies for these conditions differ. Features of four common syndromes of generalized paralysis in previously healthy patients are summarized in Table 2. The diagnostic features of the Guillain–Barré syndrome are a progressive paralysis in both legs, both arms, or all four limbs; areflexia or hyporeflexia; a cerebrospinal fluid protein level that exceeds 40 mg per deciliter (although the protein level may be normal initially), with a mononuclear-cell count of less than 10 per cubic millimeter; and a progression to peak neurologic impairment within four weeks after the onset of symptoms.8 In contrast, tick paralysis is characterized by normal cerebrospinal fluid and by a progression to peak paralysis over a period of hours to a few days. Nerve-conduction studies in patients with tick paralysis may resemble those in patients with the Guillain–Barré syndrome: findings in both conditions include prolonged latency of the distal motor nerves, diminished nerve conduction velocity, and reduction in the amplitudes of muscle and sensory-nerve action potentials, as observed in our patient. Acute lesions of the spinal cord are distinguished by sensory changes, urinary retention, fecal incontinence, and laxity of anal-sphincter tone. Poliomyelitis, with which tick paralysis was often confused 40 years ago, is now rare in North America and is usually associated with use of the trivalent oral vaccine or travel to areas where poliomyelitis is endemic. Patients with poliomyelitis usually present with fever, meningeal signs, asymmetric weakness, and a predominance of lymphocytes in the cerebrospinal fluid, all of which are absent in patients with tick paralysis. Botulism, with which tick paralysis can also be confused, is characterized by a slow, descending paralysis that involves the cranial nerves first, usually with extraocular palsy and large, poorly reactive pupils, unlike the rapid, ascending pattern of tick paralysis.9
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Neurotoxin produced by the Ixodes holocyclus tick, found in Australia, interferes with acetylcholine release at the neuromuscular junction, as does botulinum toxin.9,11,20 Extracts of homogenized I. holocyclus ticks produce paralysis when injected in dogs.21 The neurologic impairment caused by I. holocyclus ticks in Australia is more severe than that caused by dermacentor species in North America. With exposure to I. holocyclus neurotoxin, the weakness and bulbar symptoms often intensify during the first 24 to 48 hours after the tick has been removed, and clinical recovery is much slower than with dermacentor-related paralysis. For these reasons, I. holocyclus antitoxin must be administered before the tick is removed, and longer observation is required.20
The onset of tick paralysis occurs five to seven days after a female tick attaches itself to the skin. Engorgement of the feeding tick is relatively limited until it mates with a male. Mating leads to rapid engorgement, the fertilization of eggs, and the production of neurotoxin. The term "ixovotoxin" has been applied to the substance responsible for the development of tick paralysis.22 The beginning of neurotoxin production coincides with the initial paralytic symptoms in affected patients. Continued feeding by the tick apparently accelerates toxin production, accounting for the rapid clinical deterioration. Once engorgement is complete, the female tick disengages from its host and drops off to deposit the eggs. The D. variabilis tick removed from our patient deposited approximately 200 eggs 17 days after removal, an observation that supports prior claims that the fertile dermacentor female causes tick paralysis in the United States.23,24
Tick paralysis is easily confused with a variety of other conditions (Table 3).25 Ours is not the first instance in which careful examination with a fine-toothed comb led to the correct diagnosis; in other cases, patients were initially thought to have cerebellar ataxia,26 poliomyelitis,27,28 or "idiopathic paralysis."6 In each of these cases, the engorged tick was detected in scalp hair by a nurse using a comb, after extensive clinical evaluation by one or more physicians and hours to days of observation and laboratory testing.
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One case of tick paralysis involved a two-year-old child in New York who had weakness and ataxia.34 The child underwent extensive evaluation and, after observation for two days, was transferred to a tertiary medical facility, where she was found to have an engorged "wood tick" behind the right ear, at the hairline. Within 24 hours after removal of the tick the child had fully recovered. Other cases of tick paralysis include that of a two-year-old girl in Washington who had an unsteady gait and areflexia and was initially given a diagnosis of Guillain–Barré syndrome35 and that of an 18-month-old girl in Virginia who had ascending flaccid paralysis with areflexia.36 Rural residents of southern Georgia were once noted to be "so familiar with this syndrome that whenever their children or domestic animals display these symptoms, they search at once for ticks on their bodies."37
One of us has treated five cases of tick paralysis during 25 years of practice. All five of these cases were in young girls with long hair and were initially thought to be the Guillain–Barré syndrome. In two of the cases, an engorged tick was detected on the scalp by a parent or a technician during preparation for electroencephalography. In all the patients, removal of the tick was followed by clinical recovery within 8 to 24 hours. We speculate that, as in these instances, certain patients who are presumed to have the Guillain–Barré syndrome actually have undiagnosed tick paralysis and that their clinical condition may improve after the spontaneous detachment of an undetected, fully engorged female dermacentor tick.
Whenever physicians evaluate children or adults with acute ataxia or ascending paralysis, they must search carefully for engorged female ticks, primarily on the scalp but also in the axilla and perineum. A clinical diagnosis of Guillain–Barré syndrome should not be accepted until a careful search has excluded the possibility that a tick is present. One may literally have to comb for the evidence. For patients with tick paralysis, timely examination with a fine-toothed comb to detect the tick, with the use of tweezers for its removal, can result in rapid recovery and may well be one of the simplest, most effective medical interventions available.
We are indebted to Dr. Patrick F. Mongan (clinic director, Department of Family Medicine, Medical College of Georgia) for comments on the clinical aspects of the report; to Dr. Lance A. Durden (associate curator, U.S. National Tick Collection, Georgia Southern University) for insights into tick feeding and neurotoxin production; to Mr. Wesley Hobbs for photographic assistance; and to Dr. R. Philip Acuff for timely mentoring.
Source Information
From the Departments of Family Medicine (M.W.F.), Pediatrics (C.D.S.), and Neurology (T.R.S.), Medical College of Georgia, Augusta.
Address reprint requests to Dr. Felz at the Department of Family Medicine, Medical College of Georgia, HB 4032, Augusta, GA 30912, or at mfelz{at}mail.mcg.edu.
References
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