HOW USEFUL IS THE CAT SCAN FOR INVESTIGATING EPILEPSY?

Transcription

1 VOLUME 26, NO. 3 JUNE 1985 HOW USEFUL IS THE CAT SCAN FOR INVESTIGATING EPILEPSY? Isbel H Ch K P Tan Maurice H Ch Department f Radilgy Singapre General Hspital Singapre 0316 Isbel H Ch, MBBS Medical Officer Department f Radilgy Tan Tck Seng Hspital Singapre 1130 K P Tan, MBBS, FRCR, MRCP, DMRD Cnsultant University Department f Medicine It Singapre General Hspital Maurice H Ch, MBBS, MMed, MRCP Cnsultant INTRODUCTION Prir t the advent f cmputerized axial tmgraphy, patients with epilepsy in whm an anatmic diagnsis was required were ften subjected t invasive prcedures such as cranial arterigraphy r pneumencephalgraphy with their attendant mrbidity and cst. When used, the less invasive prcedure f radiistpic brain scan was ften nt very infrmative. Rutine investigatins such as plain skull radigraphy, examinatin f the cerebrspinal fluid, and even scalp electrencephalgraphy were relatively insensitive fr detectin f pathlgy. Fllwing its intrductin and subsequent wide applicatin in the past decade, cmputed tmgraphy has been increasingly used fr the clinical evaluatin f epileptic patients. The advantages were bvius. The prcedure is nn-invasive if cntrast enhancement is nt emplyed. Cnsequently, there is little r n mrbidity. It is less cstly and incnvenient fr the patient when cmpared t arterigraphy, and its images are excellent, and clearly superir t nuclear brain scans. Despite its ppularity, there have been relatively few studies evaluating the efficacy f cmputed tmgraphic head scanning fr investigating epilepsy. T address this prblem we cnducted a study t analyze the sensitivity f cmputed tmgraphy fr detecting intracranial structural disease related t the seizures. Mre imprtant, we sught t learn if the infrmatin btained frm tmgraphy was clinically useful fr influencing management. At the same time, we wanted t cmpare it with the mre basic and established electrencephalgraphic examinatin. MATERIALS AND METHODS Between February and August 1983, 160 cnsecutive patients with epilepsy underwent cmputerized axial tmgraphic (CAT) head scanning at the Department f Radilgy, Tan Tck Seng Hspital, Singapre. All scans were interpreted by trained radilgists. Frm the CAT scan request frms and reprts, we btained clinical, labratry, and scan infrmatin which were then analyzed. 283

2 SINGAPORE MEDICAL JOURNAL RESULTS The ages f the patients ranged frm 1 t 82 years. Figure 1 shws the age distributin f the patients in decade intervals. There is a bimdal distributin with peaks in the secnd and sixth decades. In additin, within each decade clumn, the patients are stacked in grups accrding t type f epilepsy. Grand mal and clinically undefined epilepsy each frmed abut tw. fifths f the ttal. The remaining ne -fifth f the patients had fcal (11.3%), tempral (7.5%), and miscellaneus (2.5%) seizures. The last grup in. cluded epileptics with petit mal and myclnus. TYPES OF FITS VS AGE NO. OF PATIENTS 7 2 GRAND MAL TEMPORAL FOCAL MISC UNDEFINED AGE DISTRIBUTION OF 160 PATIENTS ACCORDINGG TO TYPE OF EPILEPSY DECADE TYPES OF FITS GRAND MAL 40.0 TEMPORAL 7.5 FOCAL 11.3 MISC 2.5 UNDEFINED 38.8 FREQUENCY OF TYPES OF EPILEPSY IN 160 PATIENTS MISC = ft(iscellaneous 264

3 VOLUME 26, NO. 3 JUNE 1985 :Figure 3 illustrates the frequency f abnrmal CAT scans, abnrmal scalp electrencephalgrams (EEG), r bth, in the study ppulatin. 25% had nly CAT scan abnrmalities while 15% had nly EEG abnrpf s f CAT and EEG es ad furrtherscan 56% (9 patients). Hwever,ll were P nly 3 f the 9 patients in this grup shwed anatmic between CAT scan and EEG lcalizatin. crrelatin Bth CAT scan and EEG were nrmal in 54.4% f the patients. Fr the 49 patients with CAT scan abnrmalities, Figure 4 depicts the incidence f varius CAT scan diagnses in the different grups f epilepsy. Infarc- tin (18 patients), atrphy (11 patients), and hydrcephalus (5 patients) were the cmmnest diagnses. Other abnrmalities gruped as "miscellaneus" included neplasms, sequelae f trauma and surgery, and marked calcificatin. The pattern f abnrmalities in grand mal and undefined epilepsy appear similar suggesting that the grup with undefined seizuers were largely patients with undiagnsed grand mal. Althugh miscellaneus abnrmalities appear t cnstitute a large prprtin f thse with tempral and fcal epilepsy, the abslute numbers are t small fr meaningful analysis. ABNORMAL CAT OR EEG CAT ABN 25.0 BOTH ABN 5.6 EEG ABN 15.0 BOTH NORM 51.1 FREQUENCY OF CAT OR EEG ABNORMALITIES IN MO EPILEPTICS ABN - ABNORMAL NORM = NORMAL FIT DIAGNOSES GRAND MAL TEMPORAL FOCAL MI SC EMIT I,I1lN HMI _, INFARCT ATROPHY HYDRriCEPH MI<C CAT SCAN DIAGNOSIS FOUND COMPARED TO TYPES OF EPILEPSY UNDEFINED 11I SC r f1iscellaneolis q

4 SINGAPORE MEDICAL JOURNAL The pickup rates f abnrmal CAT scans and EEGs in the different grups f epilepsy are shwn in Figures 5A and 513 respectively. Althugh a trend twards a higher pickup rate f abnrmal CAT scans in fcal epilepsy cmpared t grand mal is apparent in Figure 5A, the difference is nt statistically significant (p between 0.05 and 0.10). The number f patients with tempral epilepsy and abnrmal CAT scans is t small fr statistical cmparisn. It is clear frm Figure 513 that there are n significant differences in the EEG pickup rate. EFFECT OF FIT TYPE GRAND MAL CAT NORM IIIIIIII CAT ABNORM FOCAL MIR EFFECT OF TYPE OF FITS ON INCIDENCE OF POSITIVE CAT SCAN TEMPORAL IF If I 83 3 ill I EFFECT OF FIT TYPE GRAND MAL EEG NORM EEG ABNORM FOCAL 22 2 EFFECT OF TYPE OF FITS ON INc:LDENCE OF POSITIVE EEG TEMPORAL '5 0 -'

5 VOLUME 26, NO. 3 JUNE 1985 In Figure 6A and 6B, the pickup rates f abnrmal :CAT scans and EEGs are cmpared between patients divided int 3 clinical grups: thse with nly a histry f fits; thse with additinal abnrmal histry such as paresthesia, mental retardatin, and behaviur change; and thse with abnrmal clinical signs such as hemiparalysis, papilledema, and hyperreflexia. The pickup rate f abnrmal CAT scans (Figure 6A) is significantly higher in thse with abnrmal signs cmpared t thse with fits nly (p less than 0.001), and thse with additinal abnrmal histry (p less than 0.05). The difference between thse with additinal abnrmal histry and thse with fits alne is nt statistically significant. There are n significant differences in the EEG pickup rate (Figure 66), CLINICAL FINDINGS FITS ONLY 83 8 CAT NORM CAT ABNORM HISTORY SIGNS,,:..., ,8 II MP Q I1 II INCIDENCE OF CAT ABNORMALITY IN PATIENTS WITH HISTORY OF FITS ONLY, VERSUS PATIENTS WITH ADDITIONAL ABNORMAL HISTORY ("HISTORY"), OR ABNORMAL SIGNS ("SIGNS") CLINICAL GROUP FITS ONLY 111M q EEG NORM EEG ABNORM HISTORY SIGNS 26 1 i INCIDENCE OF EEG ABNORMALITY IN PATIENTS WITH HISTORY OF FITS ONLY, VERSUS PATIENTS WITH ADDITIONAL ABNORMAL HISTORY ("HISTORY"), OR ABNORMAL SIGNS ("SIGNS") 287

6 SINGAPORE MEDICAL JOURNAL Figures 7A and 78 crrelate abnrmal CAT scan and EEG pickup rates respectively t the age f the patients classified in decades. In Figure 7A, it is evident that the CAT pickup rate increases nticeably after the furth decade. There were very few patients in the eighth and ninth decades with resultant distrtin f the trend. Cmparing the pickup rate fr patients belw 40 years ld (19.4%) with thse aged 40 yearstr mre (52.8%), the difference is highly signifi- cant (p less than 0.001). By cntrast, the pickup rate fr abnrmal EEG is higher in the yung being 70.0% in the first decade, and 15.9% fr thse lder. This difference is als highly significant (p less than 0.001). Finally, cntrast enhancement was utilized in 31 f the 160 CAT scan studies whenever the presence f abnrmality was suspected. In 25 f these, an abnr. mality was excluded; in the thers, an abnrmal finding was cnfirmed. EFFECT OF AGE CAT NORM CAT ABNOR:M 4 5 y EFFECT (1F AGE OF EPILEPTIC PATIENT ON INCIDENCE OF POSITIVE EEG 7 8 i 20 9 DECADE 0 5E1. TG EFFECT OF AGE : s.3R f G LEG NORM ABNORM EFFECT OF AGE OF EPILEPTIC PATIENT ON INCIDENCE OF POSITIVE EEG 8 9 DECADE 100.0: El

7 VOLUME 26, NO. 3 JUNE 1985 piscussion earlsd f the al in abnrmal CAT bfindings anff innect, 35.5 /t f 50 >1975reprted nn -hspitalized patients referred -:cnsecutive.because f fcal seizures diagnsed clinically, if the fits shwed fcal characteristics, r with EEG, if a fcal abnrmality was demnstrated. (1) Ail their patients had at least ne abnrmal EEG. In the fllwing year, Bachman and his clleagues reprted that structural abnrmalities n CAT scanning were identified in 28.6% f 98 children with chrnic seizure disrders. (2) Mre recently, Gilsanz et al fund CAT in abnrmalities 37.8% f 169 children with seizures and a histry f abnrmal neurlgical findings. (3) In cntrast, nly 6 (3.6%) f anther 169 children with \seizures but nrmal general andneurlgical examinatins had abnrmal CAT scans. Our study f 160 children and adults shws a similar sensitivity f CAT scans fr detecting intracranial structural disease. 30.6% f ur patients had abnrmal CAT scans. Despite the hetergeneity f the study ppulatins, it is remarkable that the prir studies and urs btained a fairly cnsistent pickup rate f abnrmal CAT 'findings in apprximately ne-third f epileptics investigated. In ur study, there were 18 patients with fcal seizures diagnsed clinically r n EEG. This subset, similar t Bgdanff's study grup, yielded abnrmal.cat findings in half (9/18). The increase in psitive 'results fr this subset (50.0%) cmpared t the general grup (30.6%) appraches statistical significance. Bgdanff als analyzed a further subset within his patients with fcal seizures wh had, in additin, predminantly fcal slwing in the EEG and fund an even higher detectin rate f 66.7%. Observing the trend, we may speculate that CAT scans are mre likely t be abnrmal in fcal seizures. especially when accmpanied by predminantly fcal slwing in the EEG. In Bgdanff's study which als included children and adults, the incidence f abnrmal CAT scans rises as the age f the seizure nset increases. This early bservatin is cnfirmed by ur larger study which shws that mre than half (52.8%) f epileptics aged 40 years r mre have abnrmal CAT scans. This cmpares with a much lwer pickup rate f 1 in 5 in thse yunger than 40. In additin, we fund the cnverse t be true fr EEG examinatin where yunger patients, particularly thse in the first decade, were mre likely t manifest abnrmalities. Clearly, the CAT scan and EEG appear t be cmplementary investigatins with lder patients having mre structural (CAT scan) disease and yunger patients having mre functinal (EEG) r structurally undetectable nes. In an bservatin similar t Gilsanz's, we nted that epileptics with abnrmal physical signs in additin t their histry f seizures were mre likely (49.2%) t have abnrmal CAT scans than epileptics with nly a histry f seizures (16.2%). In the latter grup, smetimes termed cryptgenic r idipathic epilepsy, CAT scanning is therefre less likely t be infrmative. BULLETIN OF INFECTIOUS DISEASES 26/84 REPUBLIC OF SINGAPORE S/N. DISEASES 26TH WEEK CUMULATIVE, FIRST 26 WEEKS MEDIAN Ending Ending MEDIAN CHOLERA PLAGUE SMALLPDX YELLOW FEVER CHICKENPDX DENGUE FEVER/DHF DIPHTHERIA ENTERIC FEVERS LEPROSY MALARIA POLIOMYELITIS VIRAL HEPATITIS VIRAL ENCEPHALITIS TUBERCULOSIS MEASLS Published by the Quarantine & Epidemilgy Department Ministry f the Envirnment Princess Huse Alexandra Rad Singapre

8 SINGAPORE MEDICAL JOURNAL Apart frm an increased detectin rate in the very yung, we culd nt crrelate the EEG with clinical examinatin r type f seizure. Further, there were t few patients (9) with bth EEG and CAT abnrmalities t allw significant crrelatins. Nevertheless, within this small grup, it is ntewrthy that nly 3 patients shwed anatmic agreement between EEG and CAT lcalizatin. In a different study, Oakley and cwrkers demnstrated an assciatin between CAT and clinical lateralizatin f an epileptic fcus when the EEG was nn-lateralizing. (4) The predminant CAT diagnses f infarctin, atrphy, and hydrcephalus detected in ur patients were seldm f therapeutic significance. Fr example, f the 5 patients with hydrcephalus, 4 had chrnic mental retardatin r cerebral palsy. In the grup with miscellaneus CAT diagnses, there were 5 patients with neplasms; 3 had metastases, 1 had a pituitary tumr, and 1 had a suspected meningima. Signs f crania! trauma n CAT scan were clinically bvius in 2 ut f 3 patients. Despite its mdest therapeutic utility in evaluating epileptic patients, the CAT scan, when it prvides a definitive diagnsis, reduces the need fr mre expensive, hazardus, r uncmfrtable prcedures. On the ther hand, nrmal scans are useful fr prgnsticatin. Rarely, presumed idipathic epilepsy may have a demnstrable structural cause. SUMMARY The sensitivity f CAT scan fr detecting intracranial structural disease in epileptics is apprximately 30-40%. It is higher in lder patients and thse with abnrmal clinical signs (50-60%). There is pr. bably an increased sensitivity in fcal seizures. Fr cst -cntainment, it wuld seem pragmatic t cncentrate the use f CAT scan in these high yield subgrups. The CAT scan is cmplementary t the EEG which is mre likely t be abnrmal in the yung. Althugh the therapeutic significance f CAT scan findings in epileptics is mdest, it is useful in patient management because it may prvide a definitive diagnsis and facilitate prgnsticatin. Cmpared t alternative investigatins such as cranial arteri. graphy, it is safe, virtually nn-invasive, and relatively inexpensive. REFERENCES 1. Bgdanff BM, Staffrd CR, Green L, et al: Cmputerized axial tmgraphy in the evaluatin f patients with fcal epilepsy. Neurlgy 1975; 25: Bachman DS, Hdges FJ, Freeman JM: Cmputerized Axial Tmgraphy in Chrnic Seizure Disrders f Childhd. Pediatrics 1976; 58: Gilsanz V, Strand R, Barnes P, et al: Results f Pre. sumed Cryptgenic Epilepsy in Childhd by CT Scanning. Ann Radil 1979; 22: Oakley J, Olemann GA, Olemann LM, et al: Identifying Epileptic Fci n Cntrast -Enhanced Cmputerized Tmgraphic Scans. Arch Neurl 1979; 36: