Epidemiology
- Geography: occurs worldwide
- In the US, most cases reported in Northwest USA, Rocky Mountains, and western Canada
- Age: most human cases occur in young children , <10 y/o (especially girls)
- Peak Season: April-June
Etiology
1) Dermacentor Andersoni Stiles tick: most common tick responsible
2) Dermacentor Variabilis Say (dog tick):
3) Amblyomma Americanum (the Lone Star tick):
4) Amblyomma Maculatum (the Gulf Coast tick):
5) Ixodes Scapularis (the black-legged deer tick):
Physiology
- Tick attachment (usually several days required before disease occurs) -> secretion of neurotoxin into bloodstream -> affects bulbar and spinal nuclei -> slowed motor nerve conduction (no effect on NMJ transmission)
- Mechanism: toxin probably impairs Ach mobilization at motor nerve terminal
Diagnosis
- ABG:
- CXR: normal
- CBC: normal
- LP: normal
- EMG-NCV: demonstrate slowed NCV’s and compound action potentials
Clinical
Multisystem Involvement: symptoms usually appear after tick has fed for several days
1) Neuro:
a) Progressive, Ascending Flaccid Paralysis (progresses over 24-48 hrs): first in distal LE muscles -> trunk/UE/tongue/bulbar muscles
-May be preceded by irritability or restlessness x 24 hrs
b) Acute Ataxia:
c) Absence of Sensory Changes:
2) Pulmonary:
a) Acute/Chronic Hypoventilation (see Acute Hypoventilation, [[Acute Hypoventilation]] and Chronic Hypoventilation, [[Chronic Hypoventilation]])
3) Derm:
a) Tick: usually attached to scalp (and hidden by hair), but may be anywhere on body
4) Constitutional:
a) Minimal Fever:
Treatment
Removal of Tick (gentle, steady traction with forceps/may be aided by drop of oil, petrolatum, nail polish, or other organic solvent/avoid cigarettes and other hot objects): followed by striking improvement in motor function within hrs and complete recovery within 48 hrs
-Retained mouthparts from tick may continue to secrete toxin or may form a chronic granulomatous, pruritic nodule (which may require surgical removal)
Supportive: ventilatory support as needed
Prognosis
- 10% mortality (nearly all deaths occur in cases in children)
References
- Tick paralysis: 33 human cases in Washington State, 1946-1996. Clin Infect Dis 1999; 26:1435-1439
- CDC. Tick Paralysis–Washington, 1995. MMWR 1996; 45;325-326
- Tick-borne diseases in the United States. N Engl J Med 1993; 329:936-947
- A six-year-old girl with tick paralysis. N Engl J Med 2000; 342:90-94