Electrophysiological correlates of respiratory failure in acute organophosphate poisoning: evidence for differential roles of muscarinic and nicotinic stimulation

Background. Respiratory failure in acute organophosphate (OP) poisoning can occur early and also relatively late in the clinical course, and the pathophysiology of respiratory failure at these different phases may have important clinical implications. Objective. To compare the electrophysiological findings in patients with early and late respiratory failure following acute OP poisoning. Methods. A prospective observational case series of consenting symptomatic patients with acute OP poisoning were assessed with daily physical examinations and repetitive nerve stimulation (RNS) studies. RNS was done on right and left median and ulnar nerves at 1, 3, 10, 15, 20, and 30 Hz. Outcomes such as need for ventilation and development of intermediate syndrome (IMS) were noted. Early respiratory failure was defined as occurring within 24 hours of ingestion. Results. Seventy-eight patients were recruited for the clinical and electrophysiological study and of those 59 (75.6%) patients had ingested chlorpyrifos. Seven patients developed respiratory failure within 24 hours of ingestion with overt muscarinic signs. They had no electrophysiological abnormalities at median and ulnar nerves before intubation. Three of them later developed “forme fruste” IMS. Five other patients developed late respiratory failure after 24 hours of ingestion, and all of them showed progressive RNS changes indicating severe IMS prior to intubation. Conclusion. The normal RNS in all patients developing early respiratory failure suggests that it is due to a central nervous system (CNS) and muscarinic effect. This emphasizes the need for early rapid atropinisation as a priority, combating the nicotinic effects being less urgent. This is in contrast with the late respiratory failure, which has been shown to be associated with neuromuscular dysfunction. Further studies are needed to quantify CNS and muscarinic dysfunction to assist in the development of better treatments for the severe and early OP poisoning.

Deep coma and hypokalaemia of unknown aetiology following Bungarus caeruleus bites: Exploration of pathophysiological mechanisms with two case studies

Bungarotoxin present in Bungarus caeruleus (BC) causes life threatening respiratory muscle paralysis. Deep coma and hypokalaemia have been observed in a significant proportion of patients, but the cause is unknown. We postulate the likely mechanism behind these two phenomena. We studied clinical details of two patients admitted with deep coma and performed electroencephalograms (EEG) and brain stem auditory and visual evoked potentials (BAEP and VEP). Daily serum potassium was measured along with urinary potassium excretion as a marker of total extracellular body potassium. Both patients had no brain stem reflexes on admission and the EEG revealed absent alpha and delta activity and presence of dominant theta activity. Alpha rhythm returned on the 3(rd) day in one patient, while in the other it did not, and the latter patient died on the 13(th) day due to disseminated intravascular coagulation. BAEP were delayed and VEP were absent in the deceased patient. Both had low serum potassium and low urinary potassium excretion. Replacement of potassium (up to 1.5mmol/kg/day) did not improve serum potassium and urinary potassium excretion. Absent alpha and delta activity in EEG and delayed BAEP and absent VEP are suggestive of a central action of the venom on both the cortical and brain stem neurones. Persistently low serum potassium and reduced urinary potassium excretion are suggestive of intracellular shift as the causative mechanism of hypokalaemia.

Auditory event-related potential changes in chronic occupational exposure to organophosphate pesticides

OBJECTIVE

To determine whether chronic occupational exposure to organophosphates (OP) pesticides leads to cognitive impairment using event-related potentials (ERPs).

METHODS

ERPs of 38 vegetable farmers applying OP pesticides and 35 controls were recorded using an auditory oddball paradigm. The N1, P2, N2 and P300 ERP components and the number of counting errors were compared between the groups.

RESULTS

The farmers made significantly more counting errors than controls in the oddball task. The mixed model ANOVA of component latencies revealed a significant componentxgroup interaction, suggesting farmers had a greater delay in later ERP components. Intergroup comparisons of individual components showed significant delays in N2 and P300 latencies. Subsequent ANCOVA showed significant P300 delay even after adjusting for the latency of the preceding component, N2. Intergroup differences of P300 amplitudes were not significant, although there was limited evidence of a difference in scalp topography.

CONCLUSION

Our findings indicate that chronic low-level occupational exposure to OP pesticides is associated with progressively increasing delay in successive ERP components, particularly P300.

SIGNIFICANCE

Chronic exposure to OP pesticides may delay the neurophysiological processes underlying early stages of selective attention and late stages of sensory information processing that include stimulus evaluation and updating of working memory.

Abnormal parameters of magnetically evoked motor-evoked potentials in patients with cervical spondylotic myelopathy

BACKGROUND CONTEXT

Magnetic stimulation (MS), which is used to evaluate motor pathways, is helpful in evaluating cervical spinal cord compression (cervical myelopathy [CM]). Previous studies have shown that the central motor conduction time (CMCT), which is the time taken for the nerve impulses to reach the cervical spinal roots after the stimulation of the motor cortex, is prolonged in CM. However, the duration of motor-evoked potentials (MEPs) in CM has not been studied in detail.

PURPOSE

To compare the duration, CMCT and amplitude of MEPs by MS between patients with clinical and magnetic resonance imaging (MRI) features of CM and a control group.

STUDY DESIGN/SETTING

A cross-sectional study done at Teaching Hospital, Peradeniya, Sri Lanka.

PATIENT SAMPLE

Consecutive patients with clinical features of cervical spondylotic myelopathy, without coexisting neurological abnormality.

METHODS

Transcranial and cervical spinal magnetic stimulation were performed on 21 patients with clinical and MRI features of spondylotic CM (mean age, 43.5years; range, 36-63 years; 9 men) and 17 healthy volunteers (mean age, 39.05 years; range, 23-54yrs; 6 males) using a circular coil with a Magstim 200 stimulator. MEPs were recorded over abductor digiti minimi muscle on both hands.

RESULTS

Seventeen patients had upper motor neuron (UMN) features in all four limbs; in the others, both lower limbs and one upper limb were affected. The upper limbs with UMN features had shorter duration MEPs compared with the control group. The CMCT and the total motor conduction time were also delayed in the CM group. All three differences were very highly significant (t=5.75, -3.76, 5.27; p<.001). The amplitudes showed no significant difference between the two groups (t=1.27, p=.208).

CONCLUSION

This study shows that in addition to the CMCT, the duration of MEPs is also useful in evaluating patients with CM using MS.

Long-term event-related potential changes following organophosphorus insecticide poisoning

OBJECTIVE

To determine prolonged effects of organophosphorus (OP) insecticide poisoning on cognitive event-related potentials (ERPs).

METHODS

ERPs of a group of 32 patients recovered from cholinergic phase of OP insecticide poisoning were compared with those of two matched control groups: 32 healthy volunteers and nine patients hospitalised with paracetamol overdose. A follow-up assessment was done in 21 patients (66% of the initial sample) 6 months after OP intoxication and the findings were compared with their initial ERP data.

RESULTS

Patients showed highly significant prolongation of P300 latency, compared to healthy controls (p=0.003) and the controls with paracetamol overdose (p=0.016). Follow-up ERP findings of the patients revealed that this impairment remained unchanged even 6 months after OP poisoning (p=0.790). There was no significant difference in N100, P200 and N200 latencies or P300 amplitude either among the groups or between the two assessments of the patients with OP poisoning.

CONCLUSIONS

Our results suggest that acute OP poisoning causes a delay in cognitive processes involved in stimulus classification, lasting at least for 6 months.

SIGNIFICANCE

These findings highlight the possibility of development of long-lasting cognitive deficits following OP insecticide poisoning, and warrant longer-term prospective studies to determine whether this impairment is permanent.

Cognitive processing of visual stimuli in patients with organophosphate insecticide poisoning

OBJECTIVE

To determine the effect of organophosphate (OP) insecticide poisoning on cognitive processing time of visual stimuli.

METHODS

We compared 33 patients who recovered from the cholinergic phase (on average, 15 days after poisoning) with an age- and sex-matched control group. The tests used were simple visual reaction time (SVRT), recognition visual reaction time (RVRT), visual evoked potentials (VEP), and motor evoked potentials (MEP). The term cognitive processing time (CPT) was used to denote the time taken from the initial cortical perception of a stimulus to initiation of the descending motor impulse. CPT of each type of visual reaction was calculated by subtracting the sum of the visual impulse duration and the motor impulse duration from reaction time (CPT = reaction time-[P100 latency + total motor conduction time]).

RESULTS

Both the SVRT and RVRT were significantly prolonged in patients. There was no significant difference in P100 latency or total motor conduction time (TMCT) between patients and the controls. However, CPT of simple visual reactions (CPT(SVR)) and the CPT of recognition visual reactions (CPT(RVR)) were significantly prolonged in patients.

CONCLUSIONS

Acute organophosphate poisoning may slow higher-order cognitive processing involved in visual stimulus detection and visual stimulus discrimination, even after clinical recovery from the cholinergic phase.

Routine antibiotic therapy in the management of the local inflammatory swelling in venomous snakebites: results of a placebo-controlled study

OBJECTIVE

To evaluate the value of routine antibiotic therapy in the management of the local swelling of patients with venomous snakebites.

METHODS

A prospective, placebo-controlled study at the General Hospital, Anuradhapura, Sri Lanka where 144 patients with envenoming and local swelling in the leg were allocated to receive either antibiotics (Group A = test group) or placebo (Group B = controls). Benzyl penicillin 2 mega units intravenously 6 hourly and metronidazole 500 mg by intravenous infusion 8 hourly for 5 days from the first day of the bite were given to Group A. Ethical committee approval was obtained from the Committee of General Hospital, Anuradhapura.

MAIN OUTCOME MEASURES

Circumference difference between the affected limb and the normal limb, length of the swelling measured in centimetres, and the physical characteristics of the local swelling of both groups were compared.

RESULTS

Group A had 69 patients and the Group B 75. The mean circumference difference (MCD) of the leg between the groups showed no significant difference for 4 days (P > 0.05), except at the site of the bite on the third day when the Group B showed a significant improvement (p = 0.02). There was no significant difference in the length of the local swelling or the score of physical characteristics between the two groups (P > 0.05). The proportions of recovery of the local swelling on the fourth and fifth day had no significant difference between the groups (P > 0.05).

CONCLUSION

The routine use of antibiotics (penicillin and metronidazole) does not seem to be of value in reducing the local inflammatory swelling in venomous snakebite.

Parallel infusion of hydrocortisone ± chlorpheniramine bolus injection to prevent acute adverse reactions to antivenom for snakebites

OBJECTIVE

To investigate the efficacy of continuous infusion of hydrocortisone with or without chlorpheniramine bolus against early adverse reactions to polyspecific antivenom.

DESIGN AND SETTING

Prospective, double-blind, randomised, placebo-controlled trial at General Hospital, Anuradhapura, Sri Lanka.

SUBJECTS

52 patients with snake envenoming were randomised to receive infusion of hydrocortisone (Group A), hydrocortisone with chlorpheniramine bolus (Group B) or placebo (Group C) during the administration of antivenom.

INTERVENTION

Hydrocortisone 1000 mg in 300 mL of normal saline infusion was started 5 min before and continued for 30 min after antivenom. Chlorpheniramine 10 mg intravenous bolus dose was given 5 min after commencement of antivenom.

MAIN OUTCOME MEASURES

Occurrence and severity of adverse reactions to antivenom.

RESULTS

Adverse reactions were observed in 80% (12/15) of Group A, 52% (11/21) of Group B, and 81% (13/16) of Group C. Reactions were mild or moderate except in two patients. A significant reduction in the number of adverse reactions was seen in Group B compared with the placebo group (difference, 29 percentage points; 95% CI, 0.2 to 58 percentage points). There was no significant difference between Group A and the placebo group.

CONCLUSION

Prophylaxis with a parallel hydrocortisone infusion alone is ineffective in reducing the occurrence of acute adverse reaction to antivenom serum, but combining it with chlorpheniramine seems efficacious.

Pesticide poisoning in the developing world--a minimum pesticides list

In parts of the developing world, pesticide poisoning causes more deaths than infectious diseases. Use of pesticides is poorly regulated and often dangerous; their easy availability also makes them a popular method of self-harm. In 1985, the UN Food and Agriculture Organisation (FAO) produced a voluntary code of conduct for the pesticide industry in an attempt to limit the harmful effects of pesticides. Unfortunately, a lack of adequate government resources in the developing world makes this code ineffective, and thousands of deaths continue today. WHO has recommended that access to highly toxic pesticides be restricted--where this has been done, suicide rates have fallen. Since an Essential Drugs List was established in 1977, use of a few essential drugs has rationalised drug use in many regions. An analogous Minimum Pesticides List would identify a restricted number of less dangerous pesticides to do specific tasks within an integrated pest management system. Use of safer pesticides should result in fewer deaths, just as the change from barbiturates to benzodiazepines has reduced the number of deaths from pharmaceutical self-poisoning.

Organophosphorus insecticide poisoning

Organophosphorus insecticides (OPI) are the commonest cause of poisoning in Sri Lanka. Being inhibitors of esterases, OPI cause an acute cholinergic crisis as the initial phase of neurotoxicity. The intermediate syndrome (IMS) which develops 24 to 96 hours after poisoning, and the delayed polyneuropathy (OPIDP) which manifests several weeks later, suggest a triphasic effect of OP intoxication. OPI may also cause extrapyramidal manifestations. Chronic neurobehavioural effects of longterm exposure to OPI are also a cause for concern. This paper reviews OPI poisoning in man emphasising the clinical, biochemical, and electrophysiological studies done at Peradeniya over the past two decades.

Mortality related to convulsive disorders in a developing country in Asia: trends over 20 years

The cause of death as recorded in 37125 death certificates (DC) issued in the Kandy District over 20 years at five-year intervals beginning 1967 was analysed to determine the trends in mortality caused by convulsive disorders in the community. Convulsions accounted for 881 (23.7/1000) deaths, the highest number being in infancy (35.8%). A slight male preponderance of 51.5% was observed. Most of the deaths occurred in the periphery (51.6%) and in the tea estates (36.3%) as opposed to town area (12.0%). "Febrile convulsions' was the most common diagnosis in 396 (44.9%) deaths. "Convulsions' which included neonatal and infantile convulsions accounted for 186 (21.1%) deaths. Other causes included chest complications (60, 6.8%), drowning (28, 3.2%), asphyxia (20, 2.3%), status epilepticus (19, 2.2%), burns (7, 0.8%), and poisoning (2, 0.2%). The proportion of deaths due to convulsive disorders showed a decrease from 37.28/1000 in 1967 to 9.55/1000 in 1987, which was most evident in the periphery, from 60.49/1000 to 13.19/1000. This parallelled a drop in the proportion of deaths attributed to "febrile convulsions' and "convulsions'. The study shows the need to educate the public about first-aid and the subsequent management of convulsions, especially in childhood. Health personnel in developing countries should consider it mandatory to make a specific diagnosis in children who present as febrile convulsions. Appropriate antiepileptic medication and compliance can prevent death due to status epilepticus and injuries associated with seizures.

Mortality due to poisoning in a developing agricultural country: trends over 20 years

The cause of death as recorded in 37,125 death certificates (DCs) issued in the Kandy District over 20 years at 5-year intervals beginning in 1967 were analysed to determine the trends in mortality caused by poisoning in the community. Poisoning accounted for 718 (19.3 per 1000) deaths, the highest number being in the third decade of life (41.9%). Male:female ratio was 3:1. The agent responsible for 77% of the deaths was pesticides. Acids and chemicals accounted for 6.9% of the deaths. Other poisons each contributing to less than 1% of the deaths were: plant poisons, food items, drugs, kerosine oil and alcohol. Nearly half the deaths had occurred outside the town area, at home or in small hospitals in the periphery. Mortality due to poisoning showed an increasing trend during the 20 years, from 11.8 to 43/1000 deaths, and this increase was most marked in the periphery, from 8/1000 to 70/1000. This increase paralleled the increase in suicide figures in the country. Our findings call for a shift in emphasis in public education towards first-aid management of intoxication. Health services of developing countries should provide appropriate resuscitative equipment, and ensure a regular supply of antidotes and other medication to all rural hospitals. Management of pesticide poisoning should be emphasised in the curricula for medical graduates, nurses, and paramedics.

Extrapyramidal manifestations complicating organophosphorus insecticide poisoning

Six patients who developed extrapyramidal manifestations following poisoning with the organophosphorus (OP) insecticide fenthion are reported. The extrapyramidal features, in order of frequency, were dystonia, rest tremor, cog-wheel rigidity, and choreo-athetosis. The delay in onset of these signs, following poisoning, varied from 4 to 40 days, and they disappeared spontaneously in about 1 to 4 weeks in those who survived. The human extrapyramidal system is rich in cholinergic neurons and acetylcholinesterase (AChE). Inhibition of AChE by fenthion, which has ready access to central neurons on account of its lipid solubility, is postulated as the mechanism underlying the extrapyramidal manifestations.

Absence of anti-Purkinje cell antibodies in patients with cerebellar ataxia following falciparum malaria

Immunological mechanisms have been implicated in the pathogenesis of delayed cerebellar ataxia following falciparum malaria (DCA). We tested serum and CSF samples obtained from 39 Sri Lankan patients with DCA for the presence of antibodies (Ab) directed against cerebellar Purkinje cells by an immunofluorescence (IF) technique and Western blot analysis. For the IF test 7 mu thick frozen sections of histologically normal cerebellum obtained at post mortem were used. Proteins obtained from crude preparations of Purkinje cells isolated from the cerebellum were used for Western blot analysis. Sera obtained from patients known to have antineuronal antibodies associated with cerebellar degenerations and paraneoplastic disorders (anti-Hu and anti-Yo Ab) and sera from normal blood donors served as positive and negative controls, respectively. All serum and CSF samples obtained from patients with DCA were negative for Ab directed against cerebellar Purkinje cells. Humoral mechanisms are, therefore, unlikely to be important in the pathogenesis of this delayed complication of falciparum malaria.

Hypokalaemic periodic paralysis in central Sri Lanka

We describe 14 Sinhalese male patients with hypokalaemic periodic paralysis (HPP). The age at onset was between 10 and 32 years. Each paralytic episode lasted from 6 to 48 hours (except in one patient who had an attack lasting 5 days). The frequency of attacks varied from 8 to 10 per month in one patient to only 2 attacks over a period of 16 years in another. Four patients (28.6%) had a family history of the disease. Hypokalaemia (serum potassium 1.5 to 3 mmol/l) was documented during an attack in 11 patients. No cause for hypokalaemia was evident in any of them. Investigations including EMG, thyroid hormone level and skeletal muscle histology were within normal limits between episodes. All the patients responded well to treatment with potassium supplementation, alone or with acetazolamide.

Delayed cerebellar ataxia complicating falciparum malaria: a clinical study of 74 patients

We report the clinical features of 74 patients with delayed cerebellar ataxia (DCA) following falciparum malaria, who were prospectively followed up at two centres. This unusual complication has an acute onset, with signs suggesting a predominantly midline cerebellar lesion without any evidence of cerebral involvement. There was a delay of a median 13 days between the onset of fever and the onset of ataxia. DCA has a good prognosis, with spontaneous and complete recovery within 3 months. In our opinion, it is an example of a post-infective neurological syndrome possibly mediated via an immune mechanism.

Reflex epilepsies: experience in Sri Lanka

Reflex epilepsy (RE) is characterised by seizures that are regularly elicited by some specific stimulus or event mediated by neural pathways. In a prospective study of 1287 epileptic patients seen at Peradeniya, 223 (17.3%) were found to have RE, eating being the commonest stimulus (191 patients, 85.7%). Photosensitive epilepsy (PSE) was relatively rare. Intermittent photic stimulation on 874 unselected epileptic patients produced a positive photoconvulsive response in 60 (6.9%). None had photosensitive seizures, but 3 had a higher frequency of seizures while watching television. Eating epilepsy (EE) had the highest prevalence at Peradeniya (148/1000 epileptic patients). This group was male predominant, and the onset of epilepsy in most cases was in the second decade. The majority experienced partial complex seizures. Repetitive and chronic stimulation of the amygdala during eating is suggested as the mechanism underlying EE. Twenty-one patients had seizures evoked by calculation, problem solving or spatial tasks. Juvenile myoclonic epilepsy was the commonest form of seizure disorder in them. Although PSE itself is rare, self-induced epilepsy (SIE) was common. There were 8 patients who self-induced seizures. The majority were photosensitive and they induced seizures by gazing at the sun and waving a hand in front of the eyes. In the management of REs, clobazam produced impressive results. As for possible seizure-inhibitory mechanisms, our studies on a "Sathi" mediator showed definite EEG changes during mediation. Can mediation increase the seizure-threshold and abort or prevent the propagation of the epileptic discharge? The answer, apart from its possible therapeutic applications, may provide insight into the mechanisms of seizure generation.

Classification of epileptic seizures: a hospital-based study of 1,250 patients in a developing country

The 1981 International Classification of Epileptic Seizures (ICES) was used to study the distribution of seizure types in 1,250 patients attending an Epilepsy Clinic in Sri Lanka. Based on seizure symptomatology 94.6% of the cases could be classified, and by adding the routine interictal EEG findings the percentage of classifiable seizures increased to 97%. Partial seizures (73.8% cases) were three times as common as generalized seizures (23.3% cases). Of the partial seizures, simple partial seizures (SPS) accounted for only 0.4% cases, and complex partial seizures (CPS) for 8.8%, whereas partial seizures secondarily generalized (PSGS) accounted for 64.6%. PSGS had simple onset in 12.5% and complex onset in 34.8% of cases. Myoclonic seizures were the commonest of the generalized seizures, accounting for 14.6% of all cases. Tonic-clonic seizures accounted for 7.4% of cases; absence seizures accounted for only 1.3%. The study showed the 1981 ICES to be relevant and applicable in a clinical setting with limited investigatory facilities. Difficulties encountered with regard to certain subcategories could be overcome with minor modifications which made the classification operative. Routine EEG confirmed the diagnosis in a significant number of cases but changed the diagnosis in only a few, confirming that a good standardized questionnaire is the key instrument for classifying epileptic seizures.

A scale to assess severity in organophosphorus intoxication: POP scale

We have developed a clinical scale to assess severity or organophosphorus (OP) intoxication. Five common clinical manifestations of OP poisoning have been selected as parameters, each to be assessed on a 3 point scale varying from 0-2. Poisoning can then be graded as mild (score 0-3), moderate (score 4-7) or severe (score 8-11) when the patient first presents. The scale was validated using two consecutive series of 173 patients with OP poisoning. Correlations between the scores obtained on admission and three outcome variables, namely, death, the need for ventilatory support and the dose of atropine required in the first 24 hours after admission were significant. We believe that this scale would assist in grading severity of OP intoxication at first contact and help in predicting possible outcome.

An epidemiological study of the health of Sri Lankan tea plantation workers associated with long term exposure to paraquat

Pulmonary function tests (FVC, FEV1, FEV1/FVC%, TLCO, single breath CO diffusion), chest x ray film, renal function (serum creatinine and blood urea nitrogen), liver function (serum alanine aminotransferase, aspartate transferase, and alkaline phosphatase, bilirubin, total protein, and albumin), a haematological screen (haemoglobin and packed cell volume), and a general clinical examination were performed on 85 paraquat spraymen (mean spraying time 12 years) and on two control groups (76 factory workers and 79 general workers) frequency matched for age and years of occupational service. All the subjects were men. There were no clinically important differences in any of the measurements made between the study group and the two control groups. In particular the results of the lung function tests, appropriate for paraquat toxicity of the study group, were similar to those of the control groups. The same was true of blood tests for liver and kidney function. The incidence of skin damage, nose bleeds, and nail damage in the study group was slightly higher than in the control groups but lower than the incidence reported for paraquat workers in previous studies. The results of this study confirmed that long term spraying of paraquat, at the concentrations used, produced no adverse health effects, in particular no lung damage, attributable to the occupational use of the herbicide.

Epidemiology of epilepsy in developing countries

Epilepsy is an important health problem in developing countries, where its prevalence can be up to 57 per 1000 population. This article reviews the epidemiology of epilepsy in developing countries in terms of its incidence, prevalence, seizure type, mortality data, and etiological factors. The prevalence of epilepsy is particularly high in Latin America and in several African countries, notably Liberia, Nigeria, and the United Republic of Tanzania. Parasitic infections, particularly neurocysticercosis, are important etiological factors for epilepsy in many of these countries. Other reasons for the high prevalence include intracranial infections of bacterial or viral origin, perinatal brain damage, head injuries, toxic agents, and hereditary factors. Many of these factors are, however, preventable or modifiable, and the introduction of appropriate measures to achieve this could lead to a substantial decrease in the incidence of epilepsy in developing countries.

Neurological complications of malaria

This paper reviews the neurological complications of malaria. Cerebral malaria, the acute encephalopathy which complicates exclusively the infection by Plasmodium falciparum commonly affects children and adolescents in hyperendemic areas. Plugging of cerebral capillaries and venules by clumped, parasitized red blood cells causing blood sludging in the capillary circulation is one hypothesis to explain its pathogenesis. The other is a humoral hypothesis which proposes a nonspecific, immune-mediated, inflammatory response with release of vasoactive substances capable of producing endothelial damage and alterations of permeability. Cerebral malaria has a mortality rate up to 50%, and also a considerable longterm morbidity, particularly in children. Hypoglycemia, largely in patients treated with quinine, may complicate the cerebral symptomatology. Other central nervous manifestations of malaria include intracranial hemorrhage, cerebral arterial occlusion, and transient extrapyramidal and neuropsychiatric manifestations. A self-limiting, isolated cerebellar ataxia, presumably caused by immunological mechanisms, in patients recovering from falciparum malaria has been recognized in Sri Lanka. Malaria is a common cause of febrile seizures in the tropics, and it also contributes to the development of epilepsy in later life. Several reports of spinal cord and peripheral nerve involvement are also available. A transient muscle paralysis resembling periodic paralysis during febrile episodes of malaria has been described in some patients. The pathogenesis of these neurological manifestations in malaria remains unexplored, but offers excellent perspectives for research at clinical as well as experimental level.

Does pralidoxime affect outcome of management in acute organophosphorus poisoning?

Acute organophosphorus (OP) poisoning is usually treated with atropine plus cholinesterase reactivators such as oximes, but controlled trials to assess the efficacy of oximes in OP poisoning have not been done. A period when the acetyl cholinesterase reactivator pralidoxime chloride was not available in Sri Lanka gave us the opportunity to compare atropine alone for treatment of moderate to severe OP poisoning (21 patients) with atropine plus pralixodime (24 patients). Outcome, as assessed clinically, was similar in the two groups. These results cast doubt on the necessity of cholinesterase reactivators for treatment of acute OP poisoning.

Neurological manifestations of malaria

The involvement of the nervous system in malaria is reviewed in this paper. Cerebral malaria, the acute encephalopathy which complicates exclusively the infection by Plasmodium falciparum commonly affects children and adolescents in hyperendemic areas. Plugging of cerebral capillaries and venules by clumped, parasitized red cells causing sludging in the capillary circulation is one hypothesis to explain its pathogenesis. The other is a humoral hypothesis which proposes nonspecific, immune-mediated, inflammatory responses with release of vasoactive substances capable of producing endothelial damage and alterations of permeability. Cerebral malaria has a mortality rate up to 50%, and also a considerable longterm morbidity, particularly in children. Hypoglycemia, largely in patients treated with quinine, may complicate the cerebral symptomatology. Other central nervous manifestations of malaria include intracranial hemorrhage, cerebral arterial occlusion, and transient extrapyramidal and neuropsychiatric manifestations. A self-limiting, isolated cerebellar ataxia, presumably caused by immunological mechanisms, in patients recovering from falciparum malaria has been recognized in Sri Lanka. Malaria is a common cause of febrile seizures in the tropics, and it also contributes to the development of epilepsy in later life. Several reports of spinal cord and peripheral nerve involvement are also available. A transient muscle paralysis resembling periodic paralysis during febrile episodes of malaria has been described in some patients. The pathogenesis of these neurological manifestations remains unexplored, but offers excellent perspectives for research at a clinical as well as experimental level.

Disorders of neuromuscular transmission due to natural environmental toxins

A variety of natural toxins of animal, plant, and bacterial origin are capable of causing disorders of neuromuscular transmission. Animal toxins include venomous snakes and arthropods, venoms of certain marine creatures, skin secretions of dart-poison frogs, and poisonous fish, shellfish, and crabs. There are plant poisons such as curare, and bacterial poisons such as botulinum toxin. These act at single or multiple sites of the neuromuscular apparatus interfering with voltage-gated ion channels, acetylcholine release, depolarization of the postsynaptic membrane, or generation and spread of the muscle action potential. The specific actions of these toxins are being widely exploited in the study of neuromuscular physiology and pathology. Some toxins have proved to be valuable pharmaceutical agents. Poisoning by natural neurotoxins is an important public health hazard in many parts of the world, particularly in the tropics. Poisoning may occur by a bite or a sting of a venomous animal, or by the ingestion of poisonous fish, shellfish or other marine delicacies. Contaminated food is a vehicle for poisons such as botulinum toxin. Clinically, a cardinal feature in the symptomatology is muscle paralysis with a distribution characteristic of myasthenia gravis, affecting muscles innervated by cranial nerves, neck flexors, proximal limb muscles, and respiratory muscles. Respiratory paralysis may end fatally. This paper reviews from the clinical and pathophysiologic viewpoints, naturally occurring environmental neurotoxins acting at the neuromuscular junction.

Familial eating epilepsy

Eating-related seizures affecting 20 individuals among 59 siblings belonging to nine families are presented. The type of epilepsy was partial in all the affected individuals, and the seizures complex in 15 and simple in 5, secondarily generalized in the majority. The onset of epilepsy, in most cases, was in the second decade of life. A remarkable degree of intra-family consistency was observed with regard to age at onset, symptomatology of seizures and timing of eating seizures. The study demonstrates sibling clustering in a partial epilepsy, implicating for the first time genetic susceptibility in the aetiology of eating epilepsy.

'Eating epilepsy'--a reappraisal

One hundred and fifty patients with eating seizures were detected over a 9 year period in two hospital clinics in Sri Lanka. The clinical and EEG features of 120 of them are compared to a control group of 120 patients with epilepsy. Patients with eating seizures showed a male predominance of 3:1. In more than 50% the onset of epilepsy was in the 2nd decade of life. A family history of epilepsy was obtained in 28.3% and 21 siblings themselves had eating seizures. The seizure type was simple or complex partial, secondarily generalised seizures were common. The EEG in 71.6% showed spikes, sharp/slow waves, focal in the temporal areas. The response to medication of eating seizures was similar to that of controls. Clobazam used in 17 patients as monotherapy or adjuvant therapy proved useful. The very high prevalence of eating epilepsy in the present series could pathogenically be related to genetic or ethnic factors and to the bulky meals rich in carbohydrates consumed by the patients.

Epilepsia arithmetices revisited

Three patients whose epileptic seizures are precipitated by arithmetic calculations are reported and their clinical and EEG features analysed along with those of 7 previous cases. The seizure disorder, in general, was characterised by an onset, in adolescence, of myoclonic jerks with or without tonic-clonic seizures and generalised bisynchronous 2-5 Hz spike-and-wave discharges in the EEG. Problems involving processing of spatial information were among the tasks which induced the dysrhythmia. The specificity and the consistency of the seizure-provoking stimuli suggest that in these patients the cortical areas responsible for calculations and related functions are abnormally hyperexcitable and the repeated stimulation during cognitive activities triggers seizure discharges. Two or our patients responded well to clobazam during a follow-up period of 6 months.

Acute organophosphorus insecticide poisoning during pregnancy

Intoxication with organophosphorus insecticides following ingestion with suicidal intent in two patients who were in the second and third trimesters of pregnancy is reported. Successful management of the cholinergic and intermediate phases of poisoning enabled each pregnancy to proceed to term and end in normal vaginal delivery of a healthy baby.

Acute organophosphorus insecticide poisoning in Sri Lanka

Records of 92 cases of acute organophosphorus (OP) insecticide poisoning were analysed. Of the patients 91% were under 30 years of age and 86% were males. The common agents were Dimethoate, Methamidophos, Malathion, Monocrotophos and Fenthion. Poisoning was due to ingestion with suicidal intent in the majority. In addition to the acute cholinergic features, the other important manifestations were delayed onset respiratory paralysis and delayed polyneuropathy. The overall mortality was 18%.