ORIGINAL PAPERS / ARTICLES ORIGINAUX
CEREBRAL MALARIA: CLINICAL FEATURES AND DIAGNOSIS
Celebral Malaria is the most important course of P.falciparum infection with mortality rates of up to 50%. The clinical criteria consist of unarousable coma, exclusion of other encephalopathies and the confirmation of P.falciparum infection. Beside unarousable coma in up to 80% epileptic seizures are observed in cerebral malaria. Frequently other organs are involved parallel dysfunction. The golden standard of therapy for severe P.falciparum malaria, incl. cerebral malaria, is intravenous quinine dihydrochloride. Although anticonvulsive therapy is recommended, there is no real scientific proof that such therapy in cerebral malaria given prophylactically will improve the outcome. The same applies to low molecular weight dextrane, full scale heparinisation or dexamethasone, pentoxifylline, given as adjuctive therapy, possibly provides a therapeutic value in cerebral malaria.
Besides the mortality rate, neurological sequelae until recently often denied, can occur on average in up to 7% of patients with cerebral malaria, protracted convulsions prolonged coma and severe anemia being frequently associated with the development of neurological sequelae.
Keywords : Cerebral Malaria, diagnosis clinical features
La paludisme cerebral est la plus importante complication de l’infection a P. Fqfciparum. Sa mortalite depasse 50%. Les criteres cliniques reposent sur un coma profond, l’elimination d’autres encephalopathies et la confirmation de l’infection
Par P. falciparum. Au cours du coma, on observe don 80% des cas des crises d’epilepsie. D’autres organes sont consrnes en fonction de l’atteinte cerebrale. La regle d’or du traitement du paludisme a P. falciparum et du paludisme cerebral est le dihydrochloride de quinine intaveineux. Bien que le traitement anticonvulsif soit recommended il n’y a pas de preuve scientifique que dans ce cas un tel traitement soit benefique. Il en va de meme pour la dextrane de faible poids moleculaire, l’heparinisation a dose elevee ou la dexamethasone. La pentoxifylline en traitement d’appoint du paludisme cerebral presenterait un certain interet. En plus de la mortalite des sequelles neurologiques souvent contestees encore recemment peuvent apparaitre. 7% des patients atteints de paludisme cerebral avec coma profond, convulsions prolongees et une anemic importante sont frequemment atteints de sequelles neurologiques.
Malaria represents the leading parasitic disease in today’s world (1). Half of the population of the globe is at risk to malaria and the infected population may exceed 300 million (2). Per year more than one million die from malaria, most of them from cerebral manifestation (3). Cerebral malaria (C.M.) is the most important course of Plasmodium falciparum infection with mortality rates of up to 50% (4-6).
However it is not merely a disease of tropical countries, it is seen in all its clinical aspects in all parts of the world, frequently taking a more serious course in northern countries due to delay of diagnosis and specific therapy (7,8).
Celebral malaria is an acute febrile and mainly diffuse encephalopathy, occurring in a patient infected with Plasmodium falciparum (9).
The World Health Organisation Malaria Action Programme proposed three criteria for the diagnosis of cerebral malaria:
There is frequently severely impaired function of other organs. Parameters with indirect influence onto the brain function are:
Metabolic, circulatory functions may be severly disturbed, additionally there might be acute pulmonary edema and hematological dysfuntion as well as severe impairment of coagulation (11-14).
DIAGNOSIS AND DIFFERENTIAL DIAGNOSIS OF CEREBRAL MALARIA
Cerebral malaria is the most severe and common complication affecting up to 7% of all P. falciparum malaria cases (3,5,6, 15). Twenty to fifty percent of deaths from P. falciparum malaria are reported to be due to the involvement of the central nervous system (3,5, 15). In non-immune individuals C.M. occurs at all ages, but in holoendemic areas it mainly strikes children less than five years old, the peak frequency being between the second and third year of age (3-6). A seasonal distribution of C.M. can be observed, in particular in rural tropical areas with a clear peak in incidence at the end of the rainy season (3-6).
Incubation period, or the interval between the infecting mosquito bite and the elevation of temperature above 37.8, is 11-14 days in P. falciparum infection. It correlates directly with the primary hepatic phase of the infection following sporozoite invasion of the hepatic cells. However, the incubation period is quite variable, depending on the infecting parasite strain, the type, dose and frequency of any chemoprophylactic agents taken by the patient and the type of exposure to malaria (mosquito, transfusion, congenital). Initial attacks of P. falciparum may be suppressed for weeks to months (16). During 1980 and 1981 the interval between entry into the United States and onset of P. falciparum disease exceeded 1 month in one quarter of the patients (17). Incubation periods have also varied widely in reported cases of transfusion malaria ranging from 4.to 17 days (18). In congenial malaria the onset of symptoms usually occurs 3 to 8 weeks after birth (16).
Initially patients often complain of unspecific symptoms, even days before the onset of the paroxysm: malaise, headache, myalgia and fatigue are easily mistaken for beginning viral illness (16). Children usually experience an abrupt onset, frequently with hyperpyrexia, headache, restlessness and vomiting. Within hours but sometimes much slower features of CNS involvement set in (3-6, 16).
Characteristic malaria paroxysms have 3 stages
Duration of paroxysms usually is 3 to 6 hours. In malignant falciparum malaria however an asynchronous cycle of parasite multiplication leads to continuous, remittent or irregular fever, typical paroxysms occurring only in a minority of patients.
Table 1: List of disease process in cerebral malaria
Cerebral malaria is defined as febrile and mainly diffuse encephalopathy, impairment of conciousness being a prominent feature. Unarousable coma may be preceded by severe headache, confusion, drowsiness and in many instances convulsions. It is not possible to differentiate the immediate postictal state from beginning cerebral malaria, but if coma persists for more than six hours after a convulsion in a child with P. falciparum malaria then cerebral malaria should be diagnosed (10).
Neurological signs of C .M. are those of symmetrical upper motor neuron and brain stem disturbances including dysconjugate gaze, decerebrate and decorticate postures ( 3-6, 15 ) resembling and frequently paralleling the development of midbrain syndrome (6). In a series of 66 Tanzanian children, 73% presented – at the time of admission – with unarousable coma and 15% had an organic psychosyndrome with confusion, disorientation and restlessness. Almost a quarter showed localizing signs. Two thirds of the children had generalized or – rarely – focal seizures frequently heralding the development of coma, i.e.C.M. (6). In 52 of 65 Malawian children (80%)convulsions have been observed before admission (19). In Thai patients seizures were estimated to occur in one third of the mainly adult C.M. patients (15). Meningeal irritation is rare, as are extrapyramidal or cerebellar signs (36, 15). Infrequently retinal hemorrhages and exudates are observed (20), Hyperpyrexia and splenomegaly are frequently extracranial physical findings. Less often hepatomegaly is present, frequently associated with severe anemia and high output congestive heart failure (16). In advanced disease severe anemia, icterus, renal failure, acute pulmonary oedema, heart failure, bleeding tendencies and spontaneous hemorrhages (e.g. from the upper gastrointestinal tract) and hypoglycemia complicate the course of P. falciparum (10, 21). A mainstay in diagnostic C.M. is to take careful history, in particular as to exposure of the parasite-descendance from or travelling to endemic areas as – in rare instances – transfusion of infected blood.
ROLE OF TESTING IN DIFFERENTIAL DIAGNOSIS:
The diagnosis of C.M. – principally a clinical one based on the definition excluding all other causes is deemed to be « definite » if asexual forms of P. falciparum are found in the peripheral blood smear. Thick blood films are stained with Field’s A and B stain and thin films with Leishman’s stain, Giemsa staining being equally appropriate and superior for speciation (10,22). Although a higher density of parasites appears in circulation during fever paroxysms as schizonts burst and release merozoites it is important that blood films are obtained several times daily and for several days to establish the diagnosis in patients with low density infections, which do not preclude cerebral involvement (10,16,22). Mixed infections can occur if more than 2% of the erythrocytes are infected. P. falciparum should be suspected (22). Gametocytes of P. falciparum are distinct and crescent – shaped.
Quantification of parasitemia should be done: parasites are counted against 200 leucocytes in thick film, or as percentage of 500-red blood cells in thin film (22). While high parasite-densities can be equated with severity the reverse is not always true, particulady in non-immune individuals. Any parasitemia above 250.000/m1 or more than 5% of red cells has to be considered as medical emergency. Serum antiplasmodial antibodies (immunoglobulins A,M and G class) synthesized in P. falciparum malaria have no place in the diagnosis of cerebral malaria (23). Lumbar puncture has to be done to exclude meningitis and encephalitis, although meningeal irritation is uncommon in C.M.. Cell count and protein content in CFS is usually within normal limits as well as opening pressure, although recent reports (24) indicate that patients with poor outcome tend to have elevated opening pressure in spinal tap. The search for even more sensitivity and specificity in diagnosing life-threatening malaria has lead to the development of diagnostic DNA probes for P. falciparum (25,26). The golden standard however is still the direct parasitological diagnosis by means of blood smear examination.
NATURAL HISTORY OF SEVERE P. FALCIPARUM MALARIA
A primary attack of P. lalciparum in a non immune patient is short, severe and often fatal if not treated (approximately 25%). Up to 7% develop C.M., its mortality rate ranging from 2 to 38%, the average in 15 published series being 18.6% (282/1513) (19). If the patient survives, in an untreated infection the illness usually subsides within several weeks.
Recrudescence of latent blood stages occur for up to one year, rarely longer. Contrary to other plasmodium species, there is no latent hepatic phase in P. falciparum malaria. Neurological long term sequelae do exist, convulsions and localizing signs being the most prominent features (7%=106/1513)(9).
DISEASE SPECIFIC SEVERITY SCALES
In C .M. initial neurological findings and the degree of parasitemia determine the severity and, hence, the course of disease.
Molyneux et al adapted the Glasgow Coma scale for cerebral malaria children with a minimum of O and a maximum of 5 points (4 or less is abnormal). It uses motor and crying responses to pain and includes the ability to watch (5).
The same authors developed a bedside prognostic index based on age. coma scoring, absence of corneal reflexes. signs of decerebration, witnessed convulsions, blood-glucose, white blood cell count and parasitemia, positive predictive value for an unfavorable outcome was 83%, sensitivity was 66% (5).
The level of parasitemia parallels the severity of CNS affection as well as involvement of other organs and metabolic derangements leading to secondary affection of the central nervous system. Parasitemia in more than 5% of erythrocytes is considered a medical emergency. The parasitemia is expressed in thin films in terms of percentage of erythrocytes being parasitized. In using thick film methos that parasites are counted against 500 leucocytes (22).
ACUTE TREATMENT DECISIONS
There are a number of classes of antimalarials, each of which may have an effect on a different stage of the parasite and different species.
Table 2: Classes of antimalarials
* those which can be of use for cerebral malaria are marked with an asterix modified according to Holtmann, 1986 (27)
Hoptension – cardiac failure
Table 2 denotes the classes of antimalarials with specific reference to it’s cerebral manifestations (27). Rapid reduction and clearing of parasitemia require blood schizontocidal drugs, i.e. antimalarials which are effective against the erythrocytic, asexual stage of the parasite..Antiimalarial treatment has to be initiated at the earliest possible point of disease. Intravenous quinine dihydrochloride has been and still is the golden standard of therapy for severe P. falciparum malaria inclusive C.M. (28). A loading dose of 20 mg salt/kg body weight is given over 4 hours by intravenous infusion, maintenance dosage is 10mg salt/kg body weight by i.v. infusion (2-4 hours duration at 8 hours intervals (29). At least seven days « treatment » should be completed. Where available, intensive care monitoring and appropriate nursing care are mandatory. The blood glucose concentration is checked frequently to avoid hypoglycemia. Acute renal failure prompts early dialysis; exchange blood transfusion, if considered in case of severe parasitemia, is recommended as early as possible. Convulsions, being an important cause of morbidity and mortality and being associated with poor prognosis (10,30) are to be contained as strictly as possible, however there is no real scientific proof that anticonvulsive therapy in cerebral malaria given prophylactically will improve the outcome (31 ). Neither low molecular weight dextrane, heparinization or dexamethasone have been proven efficacious in C.M. (32,33), pentoxifylline therapy, however suggests a possible therapeutic value in C.M. (34).
Neurological sequelae, until recently often denied (15) occur in an avarage of 7% of patients with cerebral malaria (3-6,19,30). Death rates range trom 5 to 38% with an avarage of 18,6%. Epileptic seizures, both focal and generalized, and focal neurological signs, like hemiplegia or aphasia, are most frequently observed, in few cases blindness, cerebellar ataxia and diffuse psychoorganic syndrome and even decerebrate state (35) might ensue. The development of neuroplical sequelae is associated with protracted convulsions, proplonged coma and sever anaemia (19). Some of these deficits resolved at least partially even months after the acute disease.