The signs and symptoms of scorpion envenomation
The human nervous system can be divided, primarily for purposes of description, into two main parts, the central nervous system and the peripheral nervous system1. The central nervous system consists of the brain itself and the spinal cord which runs down the spinal column while the peripheral nervous system is made up of the cranial and spinal nerves and the ganglia associated with such nerves. Very simply, the central nervous system can also be considered to be the voluntary (or somatic) nervous system1. An additional nervous system also exists in the human body, known as the autonomic (or involuntary) nervous system, which has two components, the sympathetic and the parasympathetic nervous systems1. The function of the sympathetic nervous system is to serve a preparatory role for the body to respond to an emergency (the fight or flight response) which includes increased heart rate, constriction of blood vessels to the skin and intestine with dilation of blood vessels to the muscles, raised blood pressure, pupil dilation and inhibition of smooth muscles in the bronchi, intestine and bladder wall. The parasympathetic nervous system, on the other hand, is directed at conserving and restoring energy levels (digest and reset response). Heart rate is reduced, pupils constrict, peristalsis and glandular activity is increased, sphincters are relaxed and the bladder wall contracts1. Nerve impulses pass along a nerve until the impulse reaches a synapse (a join or junction in the nerve fibre) when neuro-transmitters are liberated that pass the nerve impulse from the one nerve fibre to the next. Such neuro-transmitter release (and uptake) is dependent on ion channels which exist in the nerve endings (Ca+, Na+ and K+ ion channels). It is these ion channels that are primarily affected by scorpion venoms2.
The clinical presentation of scorpion envenomation is primarily a state of general excitability and hyperactivity of the autonomic nervous system resulting in the neuron firing spontaneously and continuously2,3. Other excitable tissue, for example heart and skeletal muscle, may also be involved3. Increased sympathetic activity may result in hypertension, increased heart rate, arrhythmia, sweating, fever and restlessness3. Parasympathetic activity includes increased salivation, lower heart rate, hypotension and stomach distension3.
While several species of scorpion are considered medically important (and are mostly of the Buthidae family) Parabuthus granulatus, and P. transvaalicus have been associated with most serious scorpion stings in South Africa3. Several factors play a role in how seriously a scorpion sting manifests in terms of the signs and symptoms experienced by the victim3, 4. The mass of the victim, the quantity of venom injected, the species of scorpion involved and the general health of the victim are all important contributors to the eventual presentation of the scorpion-sting victim. It must also be remembered that the presentation of signs and symptoms in children is dramatically different to that observed in adults4.
A symptom is a subjective feeling or departure from normal functioning that is experienced by the patient and which cannot be measured directly. In other words symptoms are verbal expressions of how the patient feels. The symptoms expressed by the victim will, of course, depend on which scorpion stung the victim. The symptoms described below are predominantly related to envenomation by the medically important scorpions, namely the Buthidae family3, 4.
Adults: The symptoms commonly presented by adult victims of scorpion sting include3-7: Severe pain at sting site, local numbness, increased sensitivity to stimuli, difficulty swallowing, weakness, muscle pain and cramps, trembling, increased salivation, anxiety, visual disturbances, difficulty in breathing, sweating, nausea and headache. More than fifty percent of the patients reported by Muller4 presented with severe pain and numbness at the site of the sting, difficulty swallowing, weakness, muscle pain and cramps, or trembling.
Children: the symptoms presented by children are similar to those presented by adults, however, Muller4 reported that severe pain, increased salivation or anxiety were the symptoms that occurred in more than fifty percent of patients.
A sign is any indication of a medical condition that can be observed (or measured) by anyone else other than the patient.
The signs that may be presented by adult and child victims of scorpion envenomation are the same and include: difficulty swallowing and speaking, tremors, evident sting mark, raised blood pressure, decreased motor power, raised temperature, incoordination, restlessness, increased salivation, sweating, droopy eyelids, difficulty breathing, retention of urine, increased heart rate and no gag reflex. The predominant signs presented by children, however, are restlessness and increased salivation3. The restlessness presented by children following scorpion sting is unique and is characterised by crying and screaming, extreme jerking of the arms and legs, thrashing movements, flailing and writhing. Muller et al3 state: “the restlessness caused by scorpionism in children has been described as extraordinary and duplicated by little else in medicine”.
The most dangerous symptom/sign of scorpion envenomation is difficulty breathing with respiratory failure being the primary cause of death in fatal cases.
It is estimated that over one million scorpion stings occur in the world annually8, 9 of which over 30 000 may be fatal8. The number of individuals stung by scorpions in South Africa is not clear, nevertheless, scorpion sting does occur here4 and people should be aware of the signs and symptoms that may manifest in an individual presenting with scorpionism, especially those of us who spend inordinate amounts of time outdoors and in the bush.
- Snell RS. Clinical neuroanatomy 6th ed. Philadelphia: Lippincott Williams and Wilkins; 2006.
- du Plessis LH, Elgar D, du Plessis JL. Southern African scorpion toxins: an overview. Toxicon 2008 51 1-9.
- Muller GJ, Modler H, Wium CA, Veale DJH. Scorpion sting in Southern Africa: diagnosis and management. Continuing medical education 2012 30. http://www.cmej.org.za/index.php/cmej/article/view/2545/2580 Accessed February 2016.
- Muller GJ. Scorpionism in South Africa. S Afr Med J 1993 83 405-411.
- Larsen N. Scorpion stings and venom. Biodiversity explorer http://www.biodiversityexplorer.org/arachnids/scorpions/stings/stings_and_venoms.htm Accessed February 2016.
- Bawaskar HS, Bawaskar PH. Scorpion sting: update. J Assoc Physic India 2012 60 46-55.
- Bahloul M, Chaari A, Dammak H, Samet M, Chtara K, Chelly H, Hamadi, ,CB, Kallel H, Bouaziz M. Pulmonary edema following scorpion envenomations: mechanisms, clinical manifestations, diagnosis and treatment. Int J Cardiol 2013 162 86-91.
- Chippaux JP, Goyffon M. Epidemiology of scorpionism: a global appraisal. Acta Trop 2008 107 71-79.
- Rafizadeh S, Rafinejad J Rassi Y. Epidemiology of scorpionism in Iran during 2009. J Arthro borne dis 2013 7 66-70.