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Acute Disseminated Encephalomyelitis with Baló-like Lesion by Scorpion Sting: Case Report
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.293487
Keywords: Acute disseminated encephalomyelitis, Baló's concentric sclerosis, demyelination, magnetic resonance imaging, scorpion sting
Association of demyelinating neurological diseases with arthropod venom is rare, being the wasp sting the most reported.[1],[2],[3],[4] Regarding scorpion stings, the most frequent neurological complication is stroke, both in its ischemic and hemorrhagic type; although cerebral edema, encephalitis, posterior reversible leukoencephalopathy syndrome (PRES), and demyelinating polyneuropathy have also been reported. However, to date and as far as we know, a neurological complication of the demyelinating type such as acute disseminated encephalomyelitis (ADEM) due to scorpion stings has not been reported.[5],[6],[7],[8],[9],[10]
We present a 29-year-old man, right-handed, from a rural area endemic to the presence and sting of scorpions, whose condition began precisely after being stung by a scorpion on the right forearm followed by paresthesias in the same limb. He did not go to the doctor immediately because he had been previously stung by scorpions without presenting symptoms. However, the next day in the morning, he awakens with right motor deficit and language impairment. He went to the hospital where a cranial computed tomography (CT) scan was performed and referred to our site as a brain infarction diagnosis. In our department, motor aphasia, disproportionate right hemiparesis of brachial predominance, as well as hyperreflexia and ipsilateral Babinski were documented. A brain magnetic resonance imaging (MRI) was performed, showing multiple supratentorial bihemispherical demyelinating lesions on white matter, being hypointense in T1 and hyperintense in T2 and “Fluid-Attenuated Inversion Recovery” (FLAIR) sequences. Also, a swollen lesion of greater size structured in layers in the left frontal white matter, adjacent to the precentral gyrus was observed [Figure 1]a and [Figure 1]b; a radiological finding characteristic of Baló's concentric sclerosis (BCS). There was no enhancement to gadolinium administration and spectroscopy was normal. After a treatment with prednisone 1 mg/kg for two weeks, patient presented marked symptoms improvement. The follow-up MRI [Figure 1]c and [Figure 1]d at six months showed reduction or evanescence of most lesions, including the Baló-like lesion, which showed cavitation data. During two and a half years of follow-up, the patient has reported no new outbreaks.
ADEM is a disease clinically characterized by multifocal neurological symptoms, together with evidence of multifocal and monophasic demyelination in neuroimaging. The first descriptions with recognition of a temporal relationship with infections date from the eighteenth century and were related to smallpox and measles; a century later, it would also be related to vaccines.[11] More recently, reports of ADEM secondary to bee and wasp stings, as well as centipede bites have been published, with an average latency of signs and symptoms 3–10 days after exposure; in the present case, a shorter latency is noteworthy, presenting with symptoms before 24 h after the scorpion sting.[1],[2],[3],[4],[12] The pathogenesis by which the venom of these arthropods causes these neurological symptoms in sensitized individuals is unknown. The proposed theories include (1) allergic reaction; (2) activation of myelin-reactive T-lymphocytes that migrate to the central nervous system (CNS), causing multifocal tissue destruction; and (3) cross-reaction between the toxin and the myelin of the CNS.[1],[2],[3],[4],[12] Neurotoxins in scorpion venom can produce massive release of cathecolamines and could create and autonomic storm in which the sympathetic and parasympathetic nervous system get overstimulated. The principal molecular targets of scorpion toxins are voltage-dependent Na, K, and Ca channels that are responsible for the action potentials in nerves.[13] Thus nerve terminals of the autonomic system and adrenal medulla are depolarized, causing massive release of neurotransmitters including catecholamines. Sympathetic overstimulation produces tachycardia, cardiac disfunction, and hypertension so severe that cause encephalopathy. Parasympathetic overstimulation results in salivation, bronchospasm, dysphagia, hypotension, diaphoresis, and pulmonary edema.[14] Scorpions venom produce inflammatory processes by the release of cytokines and other mediators (kinins, ecosanoids, platelet activation factor, nitric oxide) that regulate and amplify the immune response, induce tissue injury, and mediate the complications of the inflammatory reaction. The loss of balance between pro- and anti-inflammatory cytokines determines the degree and extend of inflammation and tissue damage.[15] The neurological complications associated with scorpion stings are described in 2%–8% of patients, with an average latency from the sting to the onset of CNS symptoms of 2–3 days, especially for thrombotic complications. Precisely, the most frequent complication is stroke, both in its ischemic (due to vasoconstriction and disseminated intravascular coagulation [DIC]) and hemorrhagic type (due to hypertensive crisis), being found in 0.5%–8% of the series reported.[5],[6],[16] Clinically, strokes have been presented as motor aphasia, multiple bilateral watershed infarcts, and Wallenberg syndrome.[16],[17],[18] Other neurological complications caused by scorpion stings besides stroke in literature are scarce. Cerebral edema is the second most frequent condition occurring in 0.21% of cases due to direct action of the neurotoxin of scorpion venom and hypertensive crisis.[6],[7] There have also been reports of cases of encephalitis due to direct action of the neurotoxin and PRES due to hypertensive crisis.[8],[9] Paradoxically, there is a report of a patient with multiple sclerosis who observed improvement after sting of a scorpion.[19] Regarding the pathogenesis of the BCS, it is believed to be due to a hypoxic/ischemic stimulus in the perivenular area (as with ADEM), which causes loss of myelin by oligodendrocyte apoptosis; in the outermost zone of this inflammatory reaction, the oligodendrocytes are conditioned to withstand the noxious stimulus; however, the aggressive progression of the lesion goes beyond this protected area, giving rise to a new demyelination outside of it. This leads to the concentric pattern of demyelination and partially conserved myelin that is characteristic of the BCS.[11],[20],[21] In our case, the proinflammatory effects of neurotoxins could lead to cytokines produce/release by the activated macrophage and glial cells, migrating centrifugally and giving the concentric demyelination pattern. Due to the distribution of the lesions and the greater association of BCS with multiple sclerosis, it is possible to speculate that the patient was a carrier of a “preclinical” demyelinating disease where the scorpion sting acted as trigger of an outbreak, presenting an isolated clinical syndrome with swollen Baló-like lesion.[22] There are reports in which wasp stings cause exacerbation of MS, otherwise, reports where symptoms are attenuated in case of scorpion stings and even with bee stings also exist.[2],[19] However, our patient continues to follow up and has not presented new findings within two and a half years. On the other hand, the CT scan and especially the advances in MRI have allowed the diagnosis of BCS alive. In T1 sequence, the BCS shows characteristic alternating isointense and hypointense concentric rings, with hyperintense lamellae in T2 and FLAIR sequences. Beyond this, the lesions by BCS or Baló-like can be multiple or present as solitary lesions, vary from one or two to multiple alternate bands of demyelination and lesions can range in size from no more than 1 cm to a large portion of the cerebral hemisphere.[20],[23],[24] In conclusion, although previously cases of ADEM caused by chilopoda and hymenoptera venom have been published, we believe that it is pertinent to now also communicate their association to scorpion sting. This case is relevant for its rapid presentation and for showing a Baló-like lesion in MRI. Therefore, in countries with a high incidence of scorpion stings such as Mexico, where around 300,000 cases occur annually according to a report published in 2014, neurologist must be warning about any sting-related neurological symptoms.[25] Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financ ial support and sponsorship Our institution is a public hospital and no financial support was required. Conflicts of interest There are no conflicts of interest.
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