Cutaneous Exposure to Cobra Venom: An Uncommon Presentation

To the Editor:

Many species of snakes exist in Singapore. Several are venomous ¹ and an encounter usually involves a bite to the victim. Rarely, cobra encounters involve spitting of venom. We report the case of a 58-year-old man with cutaneous venom exposure who presented to our emergency department. We describe his clinical presentation and subsequent management, highlighting some of the practical considerations in managing such a case.

A 58-year-old man with a history of hypertension and smoking presented at our emergency department an hour after an encounter with a snake. The snake, which had a description consistent with that of a cobra, had emerged from the bushes and spat venom at him. The patient used his left elbow to shield his eyes from the spray of venom, and subsequently, a painful skin reaction developed over that region (Figure 1). He was otherwise well and did not complain of any systemic symptoms of weakness, dizziness, headache, diplopia, nausea, vomiting, or diarrhea. Before coming to the emergency department, he had neither washed his left elbow nor applied any cream to the affected region.

Figure 1

Skin reaction from cobra venom spray.

On examination, the patient was alert and comfortable. His vital signs were unremarkable apart from slightly raised blood pressure. There was no ptosis, and his pupils were equal and reactive. He was not diaphoretic and did not exhibit drooling of saliva. Swallowing and speech were noted to be normal. Neurological evaluation did not reveal any deficits. His neck was supple, and he did not have any stridor or wheezing. His abdomen was soft and nontender with normal bowel sounds. Numerous discrete pruritic red papules were noted over his left medial elbow region and extending up to his proximal arm (Figure 2). There was no associated blistering, weeping of the skin, cellulitic, or necrotic changes. The affected arm was not swollen or tense, and the range of movement of his elbow was full, with normal neurological findings. There was no cervical lymphadenopathy or lymphangitis. A full blood count, serum electrolytes, coagulation profile, and radiograph of the left elbow were unremarkable.

Figure 2

Numerous discrete pruritic red papules extend over the left medial elbow region up to the proximal arm.

The diagnosis was that of local skin reaction to Elapidae venom. He was treated with intramuscular promethazine, oral amlodipine, and tetanus toxoid. He was admitted for observation. Six hours into the observation period, the rash was noted to have gradually coalesced and spread up his arm. He was also noted to be drowsy, but otherwise did not have any neurological deficits suggestive of elapid envenomation. There was no further deterioration in his condition, and the next morning, he was alert and returned to his baseline. A marked improvement was also noted in the appearance of the rash (Figure 3). The drowsiness was attributed to the promethazine that was given earlier, owing to the transient nature of the drowsiness. He was subsequently discharged 30 hours after his exposure, with topical steroid cream, oral antihistamines, and oral antibiotics, and was given a follow-up appointment with a dermatologist.

Figure 3

The rash was diminished on the second day.

One retrospective review of 52 patients presenting with snakebites to a general hospital in Singapore over a 5-year period from 2004 to 2008 estimated the incidence of snake bite to be about 1 in approximately 150,000 emergency department visits. ² In the same review of those patients, only 1 patient was spat in the eye by a cobra. The remaining patients claimed to have been bitten, although fang marks were seen in fewer than half of them. They presented mainly with local effects of pain (77%) and swelling (50%). Other symptoms such as nausea, vomiting, giddiness, and weakness were also reported, although relatively rarely. None of the patients had any neurological symptoms or signs.

Spitting cobras account for a large proportion of snakes that spit venom, but some nonspitting cobras and vipers have been noted to spit occasionally. ⁵ In Singapore, the most common spitting cobra is the black spitting cobra, Naja sumatrana, which is able to spit venom up to a few meters away. ³ Although not aggressive by nature, this snake can spit venom if it is cornered or threatened. Like other cobras, its venom is largely neurotoxic, although cardiotoxic and cytotoxic components may be found as well. These neurotoxins can cause patients to have progressive descending paralysis, ptosis, swallowing and speech difficulties, acute respiratory paralysis, and death due to respiratory failure. Treatment entails prompt supportive care and early administration of antivenom.

Apart from systemic effects of envenomation, local effects of the venom on the eye (snake venom ophthalmia) and inhalational effects on the lung have also been described in the literature. An article reviewing 10 patients with snake venom ophthalmia described the early clinical features as being pain, hyperemia, blepharitis, blepharospasm, and corneal erosions, with delayed treatment possibly leading to corneal opacity, hypopyon, or blindness. The patients reviewed did not have any signs of systemic envenomation apart from a patient who had transient lower motor neuron VII palsy from local spread of the venom. ⁴ Ophthalmic effects of venom have been attributed to their cardiotoxic components, which have been shown to have lytic properties on corneal and conjunctival membranes. The World Health Organization guidelines recommend against the use of topical, intravenous antivenom and topical steroids for patients with snake venom ophthalmia, and management principles include urgent decontamination by copious irrigation, use of topical analgesia, and application of prophylactic topical antibiotics.

The ability of airborne inhaled snake venom of the spitting cobra to induce asthma in snake handlers was described by Prescott and Potter, ⁵ with the underlying mechanism postulated to be that of immunoglobulin E-mediated hypersensitivity reaction to the venom. In our case, the patient had a local skin reaction to snake venom from a spitting cobra without any systemic, inhalational, or ophthalmic effects. The patient recovered well with prompt decontamination, symptomatic treatment, and oral antibiotics, without any significant sequelae.

We hypothesize that the cutaneous reaction was due to the cardiotoxic components of the venom, which may have lytic properties on skin epithelium. There may also be an element of immunoglobulin E-mediated hypersensitivity reaction involved in such cases. In managing these cases, early decontamination by irrigation of affected skin surfaces with copious amounts of normal saline, prompt administration of antihistamines, topical steroids, and oral antibiotics and close monitoring of the patient are proposed to ensure favorable outcomes.