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Although stings from wasps can cause severe allergic reactions, including anaphylaxis, neurological complications of wasp stings are rare. There are, however, various interesting case reports of acute myelitis, acute encephalitis, encephaloradiculoneuritis, optic neuropathy,1 cerebral infarction,2 and acute inflammatory polyradiculopathy.3 We report here the case of a young man who developed encephalomyeloradiculopathy after being stung by a wasp.
An 18 year old man was referred to Ramathibodi Hospital with impaired consciousness and quadriplegia. He had been stung by a wasp 16 days previously on the right cheek and had mild swelling and tenderness over this area. On the following day, he suffered from headache, fever, and nausea and was admitted to a regional hospital. Three days later, he was drowsy and had urinary retention. Then he developed a generalised tonic–clonic seizure lasting two to three minutes. He was intubated and referred to us.
At Ramathibodi Hospital, he was comatose, quadriplegic, and areflexic. A lumbar puncture was done. The CSF pressure was 360 mm H2O and fluid analysis showed mononuclear cells (9/mm3), a protein concentration of 160 mg/dl, and CSF/blood sugar concentrations of 4.38/13.38 mmol/l. CSF and serum were tested for Japanese encephalitis virus and dengue antibody with negative results. The erythrocyte sedimentation rate was 65 mm/h. Magnetic resonance imaging of the brain and cervical cord showed multiple ill defined scattered lesions of hypointense signal in T1 weighted (T1W) and inhomogeneous isohyperintense signal in T2 weighted (T2W) images involving both grey and white matter of medulla, pons, midbrain, basal ganglia, thalami, centrum semiovales, cortical grey matter, and cervical cord (fig 1). There was an absence of F waves in both median and ulnar nerves with absence of compound muscle action potentials on stimulating both tibial and peroneal nerves. Sensory nerve conduction was normal in median, ulnar, and sural nerves.
Methylprednisolone was given intravenously for five days. On the sixth day after starting treatment, he regained consciousness with limited eye movement and quadriplegia. A month later, a plasma exchange was performed. The power of the upper extremities gradually improved. Three months after admission, he was discharged with residual paraplegia with sensory level at T1 and urinary and fecal incontinence. The wasp was identified as Vespa tropica, a wasp commonly found throughout the country.
Allergic reactions to Hymenoptera stings range from local to severe systemic reactions or even death. These reactions are usually acute, beginning within minutes to hours in 76–96% of the patients. Nevertheless, there are reports of delayed responses that can occur days to weeks after the event. Of the 2606 reactions noted in the 1964 Academy of Allergy survey, 2.8% did not occur until several days after the sting. There have also been reports of neurological complications, hyperglobulinaemia, thrombocytopenic purpura, nephrotic syndrome, and hepatorenal syndrome.4 The neurological complications are infrequent but often serious and include clinical manifestations of damage to the central and peripheral nervous systems.
Means et al reported a case with a relapsing and progressive course of neurological symptoms and signs, including bilateral weakness and numbness of the arms and legs, following a sting by a yellow jacket (Vespula pennsylvanica).5 This patient had been alert and oriented throughout her clinical course but she eventually died after sudden respiratory and cardiac arrest. Necropsy revealed massive pulmonary embolism which was the cause of death. Examination of the nervous system showed areas of demyelination throughout the central and peripheral nervous system associated with necrosis and inflammatory infiltrates in the brain stem and spinal cord. This is the only previous report of encephalomyeloradiculoneuritis in the English language literature. In contrast to this case, our patient had a more fulminant clinical course with a seizure and alteration of consciousness. It appears that there are occasional reports of acute myelitis, encephalitis, and encephalomyelopolyradiculoneuritis in the Russian and Romanian literature but the abstracts of those reports were not available for review.
Maltzman et al reported two cases and reviewed five other cases of optic neuropathy after bee and wasp stings.1 Most cases had significant visual recovery after corticosteroid treatment. Bachman et al reported five cases presenting with acute inflammatory polyradiculopathy following Hymenoptera stings, with good recovery.3 Some cases had a sural nerve biopsy which showed segmental demyelination.
From early reports and our case, it appears that patients with neurological complications after Hymenoptera sting usually improve and some have complete recovery after high dose steroid treatment. According to some necropsy reports, the course of the disease, and the response to treatment, the pathogenesis—although not definitely known—could be an immune response to Hymenoptera sting. The nature and location of the sensitising agents involved in Hymenoptera are not entirely clear. The venom, venom sack, and insect body have all been shown to possess antigenic properties. Hymenoptera venom contains various non-myelin proteins or peptides that could be encephalitogenic in some individuals. The antigens of the wasp may initiate production of antibodies that would cross react with myelin basic proteins. Alternatively, the phospholipase A activity of the venom could liberate encephalitogenic basic proteins or other antigens from myelin membranes of the central and peripheral nervous systems, inducing immune reactions.5 Although definitive evidence of the relation between an envenoming sting and neurological complications is often missing, this is true of many conditions that reflect delayed immune responses. It is hoped that a more detailed systematic evaluation of the consequences of severe stings by Hymenoptera, including serological and immunological testing, will solve these problems in the future.
Competing interests: none declared
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