Chan, KH

Cheng, TS

Cheung, RTF

Fong, GCY

Ho, SL

Mak, W

Hong Kong Medical Journal

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Title An epidemiological study of motor neuron disease in Hong KongAuthor(s) Cheng, TS; Fong, GCY; Mak, W; Chan, KH; Cheung, RTF; Ho, SLCitationThe 8th Medical Research Conference (MRC 2003), Hong Kong,25-26 January 2003. In Hong Kong Medical Journal, 2003, v. 9 n.1 suppl. 1, p. 80, abstract NUS-18Issued Date 2003URL http://hdl.handle.net/10722/46692Rights Creative Commons: Attribution 3.0 Hong Kong License80      HKMJ Vol 9 No 1 February 2003 SupplementSeronegative myasthenia gravis in Hong Kong ChineseK H Chan, KL Tsang, W Mak, CY Fong, TS Cheng, RTF Cheung, SL Ho. University Department of Medicine, The Universityof Hong Kong, Queen Mary Hospital, Hong Kong.Introduction: Acquired myasthenia gravis (MG) is an autoimmune disease due to anti-acetylcholine receptorantibodies (anti-AChR) that damage nicotinic acetylcholine receptors on neuromuscular junctions. Variableproportions of generalized MG patients were reported to have undetectable serum anti-AchR level, designated asseronegative MG (SNMG) but without clear definitions of SNMG. One group reported that antibodies againstmuscle-specific kinase was the pathogenetic basis of SNMG. The exact pathogenesis of SNMG is not yet certainand genuine frequency is unknown.Methods: Patients with MG in neurology clinic were studied with clinical, radiological, serological,electrophysiological and histological data reviewed. Patients with initial negative anti-AChR had the assay repeatedat least 12 months apart from the first one, together with anti-striational antibody test. Patients with family historyof MG had EMG results repeated in details to exclude congenital MG. Patients with repeatedly negative anti-AChRbinding assays had serum tested for anti-AChR modulating antibodies (a bioassay using cultured muscel cells) andP/Q type calcium channel antibodies to look for Lambert-Eaton myasthenic syndrome. Only patients withrepeatedly negative anti-AchR binding and anti-striational antibodies, negative for anti-AchR modulating andcalcium channel antibodies, and with congenital MG excluded were defined as SNMG.Results: A total 52 MG patients were studied, 21 had pure ocular MG and 31 had generalized MG. Three hadturned seropositive upon repeated assay and 1 had positive test for modulating antibodies only. One patient withfamily history of had congenital MG upon detailed EMG. Only 2 of the 31 generalized MG patients (6.5%) wereSNMG. One of the 2 generalized SNMG patient had thymic hyperplasia. No SNMG patients had thymoma. SNMGis more common in pure ocular MG patients.Conclusion: Generalized SNMG is rare. Strigent criteria are required for diagnosis of SNMG. Thymic hyperplasia,but not thymoma, can occur in SNMG. We postulate that a subgroup of SNMG patients may have low titer of highaffinity anti-AchR undetectable by current assays.An epidemiological study of motor neuron disease in Hong KongTS Cheng, GCY Fong, W Mak, KH Chan, RTF Cheung, SL Ho. Division of Neurology, Department of Medicine, University ofHong Kong, Queen Mary Hospital, Hong KongBackground: In a previous epidemiological study conducted in 1990s, the incidence and prevalence of motor neuron disease (MND)in Hong Kong Chinese were found to be low compared to the worldwide figures. Moreover, the incidence of MND had been reported toincrease steadily over the last few decades in other parts of the world. In this communication, we reported our epidemiological data ofMND in the Hong Kong West region of Hong Kong Special Administrative Region of China and compared the results with that of theprevious study.Method: We identified the subjects from the Hospital Authority Database by searching the admission records of Queen Mary Hospital,between 1997 and 2001, using ICD-9 codes of 335. Each retrieved case record was reviewed independently by at least two neurologists.The clinical diagnosis and classification of MND were based on the revised El Escorial criteria.Results: Of 50 identified subjects, 27 subjects were recruited in the present study. Among which, 22 (81%) were definite MND and 5(19%) were probable MND. Among definite MND, 15 (68%) were limb onset. The male to female ratio was 2.8:1. All subjects wereChinese. The number of new cases from 1997 to 2001 was 22. Thirteen cases were died in this period, and 14 patients were survivingas of December 31, 2001. Therefore, the annual incidence was 4.4 with an incidence rate of 0.77/100,000/year, the point prevalence atDecember 31, 2001, was 2.4/100,000, the average annual mortality was 2.6, and the mortality rate was 0.46/100,000/year. The meansurvival time was 27.1 months (range: 7 to 65 months, SD 17.9). The mean age of onset was 51.5 years (range: 30 to 77 years,SD 11.7), with a peak observed between 55 and 59 years. Eleven cases (40%) had their disease-onset before 50 years of age.Conclusion: In this study, the incidence and prevalence of MND among Hong Kong Chinese remained low compared with theworldwide figures. However, comparing to the previous epidemiological data of MND collected between 1989 and 1992, we noticed atrend of increase in the overall incidence (148%) as well as prevalence (152%) over the last decade. Moreover, the incidence of MNDamong the younger age group was also increased. Our data warrant a territory wide epidemiological study to document the changes inMND epidemiology in Hong Kong over the last decade.Acknowledgment: This study was supported by Liu Po Shan/Dr Vincent Liu Endowment Fund for Motor Neurone Disease, Faculty ofMedicine, The University of Hong Kong (to GCYF/SLH), and by the University Department Medicine, The University of Hong Kong (to GCYFand TS Cheng).NUS-17NUS-18

An epidemiological study of motor neuron disease in Hong Kong

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An epidemiological study of motor neuron disease in Hong Kong

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