Page 23 - JSOM Summer 2019

The following morning at 1000 hours (H ), the patient was numbness have been reported from bites by various NFFC
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reexamined and enthusiastically reported that full sensation species elsewhere. 14,16 The Western purple-glossed snake (Am-
had been restored to the bitten foot and the paresthesias had blyodipsas unicolor) (Figure 3) is a small NFFC indigenous to
resolved. He was asked to perform a walk test and ambulated Benin that matches the description provided by the patient,
without difficulty; a repeat sensory exam showed a return of and the clinical effects of its venom are unknown. Two neuro-
full sensation to the dorsal and plantar aspects of the foot. toxic elapids also fit the description of the snake: the half-
His gait was normal. His WBCT remained normal at both banded garter snake (Figure 2) and the forest cobra (Figure 1),
reading times, and his vital signs remained within normal lim- both of which were captured by one of the authors within
its. Physical examination showed complete resolution of all the hospital grounds. The half-banded garter snake is a secre-
signs and symptoms. A tetanus vaccine was administered, and tive species with no serious envenomations documented, and
the patient was discharged 39 hours postenvenomation with bizarre symptoms such as transient nasal congestion were re-
instructions to return if any complications or new signs and ported in the very few case reports that exist. A forest cobra
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symptoms of envenomation developed. was deemed unlikely for precisely the opposite reason, as en-
venomations by these snakes are true emergencies character-
ized by a progressive descending flaccid paralysis ending in
Discussion
respiratory arrest. Paresthesias such as numbness and tingling
This case illustrates a number of the challenges associated are a commonly reported symptom of bites by neurotoxic el-
with snakebite medicine. Identification of the snake can pro- apids in Africa and elsewhere. 17–19 The description of the bite
vide useful information, but it can also mislead and must be as “chewing” or “tugging” is more consistent with an NFFC
interpreted in the broader context of the clinical picture. A or elapid bite than with a viper envenomation. Burrowing asps
snakebite may have come from a nonvenomous species, and possess potent cardiotoxins known as sarafotoxins, which can
even a bite from a venomous snake does not mean an enven- cause atrioventricular blocks, ST-T changes, and severe hyper-
omation has occurred. The estimated incidence of dry bites tension due to vasoconstriction in addition to the pain and
from venomous snakes varies by species; they are believed swelling that occurs in virtually all bites by atractaspids. The
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to account for 10% or less of carpet viper (Echis spp.) bites, incidence of dry bites in burrowing asps is unknown, but a
roughly 20% to 25% of pit viper bites, and up to 80% of mild envenomation was highly unlikely due to the absence of
bites from sea snakes (Hydrophiinae spp.) and Eastern brown any pain or swelling and the patient’s unremarkable vital signs.
snakes. When venom is injected, the quantity can be further
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influenced by the circumstances of the bite and clothing of the It is important to remember that just as a snakebite does
victim. The onset of progressive symptoms can be delayed not equal an envenomation, a dry bite does not necessarily
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by mechanical influences such as use of a constricting band or mean that the patient will be asymptomatic. Anxiety and in-
anatomical factors such as the location of venom injection. 1,10 creased sympathetic stimulation resulting from the event can
It is therefore critical to consider a broad range of possible di- produce somatic symptoms that mirror the early signs of a
agnoses when evaluating a snakebite patient to ensure that an- neurotoxic envenomation including the diaphoresis, paresthe-
tivenom therapy is given promptly to those who need it and not sias, and restlessness observed in our patient. In this case,
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wasted on those who do not. In most cases it would be more the patient did not receive antivenom upon arrival because his
useful for nonherpetologist clinicians to focus on identifying vital signs and WBCT were normal and he failed to present
the various syndromes of envenomation rather than the snakes, with any indications of a life- or limb-threatening envenom-
but in a case like this where the symptoms are nonspecific, a ation. While the persistence of the paresthesias after removal
more complete description of the snake could have provided of the constricting band was surprising, it was not unprece-
valuable information. Only 93 of the 400 or so snake species in dented. Psychosomatic paresthesias and even paraplegias are
sub-Saharan Africa are known to have produced clinically sig- a rare but well-documented phenomenon in other areas of
nificant envenomations in humans and roughly 30 of these spe- medicine. 22,23
cies have caused fatalities, but there are a significant number
of non-front-fanged snakes across the subcontinent with ven- It is certainly possible that the resolution of symptoms fol-
oms whose clinical effects are largely unknown. These snakes lowing placebo treatment was merely coincidental, but this
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possess venoms of varying composition but lack the highly possibility seems unlikely when considering the totality of the
derived delivery systems of the front-fanged colubroids: they evidence. The other plausible explanation we considered was a
cannot store significant quantities of venom in the gland, in- transient pressure neuropathy of the superficial peroneal nerve
ject venom at substantially lower pressures, and have grooved or tibial nerve, which have been reported following prolonged
teeth that are oriented more posteriorly along the maxilla in arteriovenous tourniquet use during orthopedic surgeries
contrast to the hypodermic-like, anteriorly positioned fangs of and can result in foot drop and paresthesias. 24,25 This did not
the front-fanged venomous snakes. Two of these species were seem likely, however, as the constricting band was not applied
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not considered dangerous until the deaths of two respected tightly enough to completely occlude distal circulation and the
herpetologists who had the unfortunate distinction of proving symptoms resolved abruptly within hours of placebo adminis-
otherwise. 14,15 There are more than 2,300 species of NFFCs tration despite a lack of any improvement in sensation during
worldwide, and roughly 350 are currently known to have pro- the preceding 24 hours. Furthermore, the paresthesias in this
duced clinically significant envenomations. That number is case were diffuse and circumferential rather than the derma-
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likely to be much higher, but many bites are probably never tomal distribution that one would expect following injury to
reported due to the remote geographic location of the patient either of these nerves. Sensory testing revealed an absence of
or relatively benign outcome of the event. sensation on both the dorsal and plantar aspects of the bitten
foot, while superficial peroneal nerve injury would cause sen-
Many NFFC species fit the physical description of the snake sory loss of the anterolateral aspect of the lower leg and most
provided by our patient, and mild local symptoms including of the foot dorsum but not the plantar aspect.

A Case of Fright or a Deadly Bite? | 21