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Biomedical subjects

K S Chan

Publications and source records attributed to K S Chan.

At least 37 records · Page 2Linked to original sources
PubMed2002

Clinical spectrum of paradoxical deterioration during antituberculosis therapy in non-HIV-infected patients.

Paradoxical deterioration during antituberculosis therapy, defined as the clinical or radiological worsening of pre-existing tuberculous lesions or the development of new lesions in a patient who initially improves, remains a diagnostic dilemma. Although different clinical presentations of paradoxical response have been described, a systematic analysis of the entity in non-HIV-infected patients is lacking. Reported here are two cases of paradoxical deterioration in which sequential changes in lymphocyte counts and tuberculin skin test results are emphasized. In addition, 120 episodes of paradoxical response after antituberculosis treatment were reviewed. Of the total 122 episodes, 101 (82.8%) were associated with extrapulmonary tuberculosis. The median time from commencement of treatment to paradoxical deterioration was 60 days. The median time to onset of central nervous system manifestations (63 days) was longer than the time to onset of manifestations at other sites (56 days) ( P=0.02). Development of new lesions in anatomical sites other than those observed at initial presentation was observed in 31 (25.4%) episodes. A surge in the lymphocyte count, accompanied by an exaggerated tuberculin skin reaction, was observed in our patients during the paradoxical deterioration, analogous to the findings in HIV-positive patients. Treatment of the paradoxical response included surgical intervention (60.7%) and administration of steroids (39.3%). The use of steroids appeared to be safe in this series, as 95% of the Mycobacterium tuberculosis isolates were susceptible to first-line antituberculosis therapy.

Abscess↗
PubMed2002

Robust design and the use of auxiliary variables in estimating population size for an open population.

We consider the problem of estimating the population size for an open population where the data are collected over secondary periods within primary periods according to a robust design suggested by Pollock (1982, Journal of Wildlife Management 46, 757-760). A conditional likelihood is used to estimate the parameters associated with a generalized linear model in which the capture probability is assumed to have a logistic form depending on individual covariates. A Horvitz-Thompson-type estimator is used to estimate the population size for each primary period and the survival probabilities between primary periods. The asymptotic properties of the proposed estimators are investigated through simulation and are found to perform well. A data set for such a robust design of a small-mammal capture-recapture study conducted at Dummy Bottom within Browns Park National Wildlife Refuge is analyzed.

Animals↗
PubMed2001

Occurrence of matrix metalloproteinases and tissue inhibitors of metalloproteinases in tuberculous pleuritis.

OBJECTIVE: Matrix metalloproteinases (MMP) and tissue inhibitors of metalloproteinases (TIMP) have been found in high concentrations in pleural effusions. Because MMP and TIMP may play a part in the causation of the fibrosis seen in tuberculous (TB) pleuritis their occurrence was examined. DESIGN: Pleural effusion fluid and plasma concentrations of MMP-1, MMP-2, MMP-3, MMP-8, MMP-9, TIMP-1 and TIMP-2 were determined by ELISA in 21 patients with TB pleuritis. To adjust for the total protein content, respective ratios were calculated. Activities of MMP-2 and MMP-9 were measured by gelatine zymography and the MMP-9/MMP-2 ratios calculated. Pleural effusions and plasma of 15 patients with congestive heat failure (CHF) and plasma of 15 healthy persons (CON) served as controls. RESULTS: Immunoreactive pleural fluid concentrations of MMP-1, MMP-2, MMP-8, and MMP-9 were higher in TB compared to CHF, but plasma concentrations were not different between the groups. TB pleural fluid concentrations of MMP-1, MMP-2, TIMP-1, and TIMP-2 were higher compared to TB plasma. MMP-3 was found in trace amounts only. The MMP-9/total protein ratios in pleural fluid were higher in TB compared to CHF (0.4492+/-0.1633 vs 0.0364+/-0.0145, P<0.005) but the TIMP-1 ratios were lower (139.0+/-28.7 vs 517.8+/-183.7, P<0.0005). In TB pleural fluid vs TB plasma, the respective MMP-1, MMP-2, TIMP-1, and TIMP-2 ratios were increased (0.46+/-0.10 vs 0.17+/-0.02; 25.2+/-2.8 vs 4.2+/-0.9; 139.0+/-28.7 vs 27.8+/-8.2; 0.67+/-0.13 vs 0.18+/-0.04, P<0.0005 each). Gelatine zymography demonstrated MMP-2 and MMP-9 bands of different brightness in TB effusions but in CHF effusions the MMP-9 band was barely visible. The MMP-9/MMP-2 effusion ratios were therefore higher in TB compared to CHF (0.46+/-0.15 vs 0.05+/-0.04, P<0.0005). CONCLUSION: Compartmentalized MMP-1, MMP-2, TIMP-1, and TIMP-2 and, compared to CHF, a surplus of MMP-1, MMP-2, MMP-8, and MMP-9 in the pleural space obviously contribute to the fibrotic reactions in TB pleuritis.

Adult↗
PubMed1999

Pattern of lymph node pathology in a private pathology laboratory.

Lymph node excision biopsy is commonly carried out for the investigation of lymphadenopathy. The objective of this study is to elucidate the pattern of nodal pathology seen in a private pathology practice. A total of 137 nodal biopsies for primary investigation of nodal enlargement were retrieved from the files in a private diagnostic pathology laboratory in the year 1997. Lymph nodes excised for cancer staging were excluded from this study. The histology was reviewed based on H&E stained sections, and with additional histochemical and immunoperoxidase stains when deemed necessary. Cases of malignant lymphomas were sub-classified with the aid of further immunophenotyping using a panel of monoclonal and polyclonal lymphoid antibodies. One case was excluded from this study due to inadequate tissue for further assessment. There were 58 males and 78 females, giving a ratio of 1:1.3 in the remaining 136 cases. They consisted of 13 Malays (M), 108 Chinese (C), 14 Indians (I) and 1 other ethnic group (O). The ratio of M:C:I:O was 1:8.3:1.1:0.1. The majority of the cases were in the age range of 20 to 50 years. The pathology consisted of 17 (12.5%) malignant lymphomas [6 Hodgkin's lymphoma, 11 non-Hodgkin's lymphoma], 35 (25.7%) metastatic carcinomas, 45 (33.1%) reactive hyperplasia, 19 (13.9%) tuberculosis, 11 (8.2%) Kikuchi's disease and 9 (6.6%) others (Castleman's disease 2, cat scratch disease 2, Kimura's disease 1, sarcoidosis 1, non-specific lymphadenitis 3). All categories of nodal disease showed approximately similar ratio of ethnic and gender distribution as above, except for Kikuchi's disease, for which 100% of the patients were female. The most common site of biopsy was from the head and neck region, particularly the cervical group of nodes. The most common nodal pathology seen in the private laboratory was reactive hyperplasia, followed by metastatic carcinoma. Malignant lymphoma constituted only 12.5% of the cases.

Adolescent↗
PubMed1998

From patterns to processes: phase and density dependencies in the Canadian lynx cycle.

Across the boreal forest of North America, lynx populations undergo 10-year cycles. Analysis of 21 time series from 1821 to the present demonstrates that these fluctuations are generated by nonlinear processes with regulatory delays. Trophic interactions between lynx and hares cause delayed density-dependent regulation of lynx population growth. The nonlinearity, in contrast, appears to arise from phase dependencies in hunting success by lynx through the cycle. Using a combined approach of empirical, statistical, and mathematical modeling, we highlight how shifts in trophic interactions between the lynx and the hare generate the nonlinear process primarily by shifting functional response curves during the increase and the decrease phases.

Animals↗
PubMed1998

Phase- and density-dependent population dynamics in Norwegian lemmings: interaction between deterministic and stochastic processes.

We analysed two 26-year long (1970-1995) time-series on annual population growth rates of Norwegian lemmings (Lemmus lemmus) from Finse, south Norway, using a threshold autoregressive (TAR) approach. We demonstrate that the population dynamics is both phase- and density-dependent. The phase-dependence accounts for the observed nonlinearity. We used the deduced stochastic model structure as a basis for evaluating the dynamic properties of this system. The dynamics is characterized either by limit cycles or chaos (the latter with a strong semi-periodic component). Stochasticity is seen to play an important role in the determination of the periodicity. The ecological implications of these statistical and mathematical results are discussed.

Animals↗
PubMed1998

Is the asthma quality of life questionnaire a useful measure for low-income asthmatics?

The purpose of this study was to evaluate the reliability and validity of the Asthma Quality of Life Questionnaire (AQLQ) in a population-based sample of low-income adults with asthma. A total of 112 subjects (46 African American, 66 Caucasian; mean age = 33 +/- 9 yr; 26% male) were recruited from the Baltimore County, Maryland and Atlanta, Georgia metropolitan areas. Internal consistency reliability (Cronbach's alpha) was high for the overall scale (0. 96); 2-wk reproducibility (intraclass correlation, ICC) was 0.82 (n = 38). Overall score was significantly correlated with FEV1 percentage of predicted (r = 0.20), and the Asthma Disease Severity Scale (r = -0.38). Correlations between overall score and the SF-36 Physical Component Summary (r = 0.49), SF-36 Mental Component Summary (r = 0.37), Cantril's Ladder (r = 0.23), and the Health Utilities Index (r = 0.22) supported the validity of the AQLQ in this sample. Comparison of reliability and validity estimates across racial groups found few substantive differences. Internal consistency, reproducibility, and validity estimates found in this sample were consistent with those of a reliable and valid measure and were comparable to those found in other populations. These results suggest the AQLQ is a useful indicator of health- related quality of life in low-income asthmatics.

Adult↗
PubMed1998

Changes in surrogate laboratory markers, clinical endpoints, and health-related quality of life in patients infected with the human immunodeficiency virus.

OBJECTIVE: To evaluate the relationship between laboratory markers of HIV, AIDS-defining events, study discontinuation, and summary scores from the MOS-HIV Health Survey. METHODS: Secondary analysis of data from a clinical trial of antiretroviral therapies in advanced HIV-infected patients (N = 940). Clinical and health-related quality-of-life data were collected over 48 weeks. Linear regression, logistic regression and survival analyses were performed to evaluate the relationships between MOS-HIV summary scores, clinical events, and laboratory markers. RESULTS: Each point increase in PHS resulted in a 3.0% decrease in the likelihood of developing an AIDS-defining event (p < .05) and a 2.7% decrease in likelihood of study discontinuation (p < .05). MHS did not significantly predict clinical events, but did predict study discontinuation (p < .05). From the linear regression analyses, the change in CD4 counts was a significant predictor of the change in MHS (p < .01). CONCLUSION: The MOS-HIV summary scores predict clinical events and study discontinuation in advanced HIV-infected patients.

Adult↗
PubMed1998

The impact of asthma on health-related quality of life.

Although a substantial body of epidemiological and economic literature on asthma exists, relatively little is known about the impact of asthma on health-related quality of life (HRQL). The purpose of this review was to synthesize results from recent studies, profile the factors influencing HRQL in asthmatics, discuss the impact of treatment on HRQL outcomes, and offer recommendations for further research. The results of this review support the premise that asthma can adversely affect the physical, psychological, and social domains of HRQL. Published data suggest that females, those from lower socioeconomic groups, and ethnic minorities experience poorer quality of life as a result of their asthma symptoms. Results of published clinical trials indicate treatment regimens can have a significant impact on HRQL outcomes. Pharmacological interventions appear to effect change primarily in the physical domain and behavioral interventions lead to improvements in both physical and psychosocial domains. Future research should focus on precise a priori delineation of research hypotheses, including the selection of primary and secondary endpoints, the clarification and consistent application of criteria for defining asthma severity, thoughtful selection of HRQL instruments appropriate for the research hypotheses and target population, and careful delineation of clinically meaningful change scores of asthma-specific outcome measures.

Asthma↗
PubMed1997

Monitoring the therapy of pulmonary tuberculosis by nested polymerase chain reaction assay.

Monthly clinical and microbiological parameters (by sputum smear, culture and PCR assay), of 50 patients with documented pulmonary tuberculosis and on anti-tuberculosis therapy, were monitored over a period of 18 months. PCR converters (70%) who had PCR conversion before the sixth month of treatment did not have clinical or microbiological evidence of failure or relapse, while nine of 15 PCR persisters (30%) had clinical failure (7) and relapse (2). The PCR persisters were significantly associated with more underlying medical illnesses, high mean radiographic scores on the extent of disease involvement, previous drug treatment, initial sputum smear positivity and multi-drug resistance. Of the eight PCR persisters infected by susceptible Mycobacterium tuberculosis, all had marked residual radiographic changes despite completion of drug therapy. The findings may have important implications in the application of PCR on individualization of the duration of anti-tuberculosis therapy.

Adult↗
PubMed1997

Adult height and incidence of cancer in male physicians (United States).

Adult height has been found in some but not all studies to be associated positively with overall cancer incidence as well as several site-specific cancers. The Physicians' Health Study (PHS), a randomized trial of beta-carotene and aspirin in the primary prevention of cancer and cardiovascular disease in men, provided an opportunity to examine the association between height and total malignant neoplasms (excluding non-melanoma skin cancer), as well as site-specific cancers including prostate, colorectal, and lung cancer. The PHS is comprised of 22,071 US male physicians in the United States, a population homogeneous for adult socioeconomic status, aged 40 to 84 years in 1982. Participants were classified into five height categories at study entry. After an average follow-up of over 12 years, there were 2,566 cases of incident total malignant neoplasms, including 1,047 prostate, 341 colorectal, and 170 lung cancer cases. Height was associated positively with both total malignant neoplasms and prostate cancer. Compared with men in the shortest category (<67 inches), relative risks and 95 percent confidence intervals (CI) for total malignant neoplasms for men whose height (in inches) was 68-69, 70-71, 72, and 73+ were, respectively: 1.13 (CI = 0.99-1.28), 1.15 (CI = 1.02-1.30), 1.29 (CI = 1.12-1.49), and 1.21 (CI = 1.05-1.39), P trend 0.001, adjusted for age, randomized treatment assignments, body mass index (wt/ht2), cigarette smoking, alcohol use, and exercise frequency. For prostate cancer, the corresponding RR values were 1.23 (CI = 1.00-1.51), 1.26 (CI = 1.04-1.54), 1.59 (CI = 1.27-1.98), and 1.26 (CI = 1.00-1.59), P trend 0.005. For colorectal cancer, in some but not all height categories compared with the shortest, there were elevated RRs without a significant linear trend: RR = 1.51 (CI = 1.06-2.14), 1.14 (CI = 0.80-1.62), 1.19 (CI = 0.79-1.80), and 1.53 (CI = 1.04-2.25), P trend 0.23. In contrast, there was no evidence of an association of height with lung cancer. These data indicate a positive association between height and risk of total malignant neoplasms, as well as of prostate cancer and, possibly, colorectal cancer.

Adult↗
PubMed1997

A three-year review of treatment of cervical intraepithelial neoplasia with large loop excision of the transformation zone.

One hundred and eighty-five patients were treated with large loop excision of the transformation zone for cervical intraepithelial neoplasia from October 1992 through September 1994. All patients were followed up regularly until September 1995 to review the outcome and morbidity. Cure rates of 97.2% in the first six months and 95.4% at the end of the first 12 months were obtained. Thirteen patients (7.0%) were admitted as emergency cases for post-operative haemorrhage, which required suturing, cauterisation with silver nitrate or electrocoagulation, vaginal douching, or antibiotic treatment. One patient developed cervical stenosis and incomplete excisions were noted in 46 (24.9%) patients. Eleven (6.0%) patients had cervical carcinomas detected. Our findings further confirm that this method is a reliable and safe way to treat cervical intraepithelial neoplasia with an acceptable rate of morbidity.

Journal Article↗
PubMed1997

A dynamic frailty model for multivariate survival data.

We consider the statistical modeling of data consisting of many study subjects with serially correlated multivariate survival responses. The (ordinary) frailty model handles the serial correlation in such data by introducing an unobserved multiplicative random effect term, called the frailty, in the hazard function. The frailties are often assumed to be identical for the survival times from the same unit. We have generalized the frailty model by allowing the frailties to vary stochastically with the indices. We have proposed a simple scheme to update the dynamic frailties. This approach assumes that the random effects are gamma distributed. At each occurrence, the two gamma parameters are updated according to the past information. In terms of their marginal distributions, the dynamic frailties form a multiplicative random walk. This approach results in a tractable likelihood. The small sample behavior of the MLE is studied via a simulation experiment. The model is then illustrated with a data set from an animal carcinogenesis experiment.

Biometry↗
PubMed1997

Conservative management of patients with histological incomplete excision of cervical intraepithelial neoplasia after large loop excision of transformation zone.

OBJECTIVE: To evaluate conservative management of patients with histological incomplete excision of CIN after large loop excision of transformation zone (LLETZ). METHODS: Two hundred and seventeen patients with high grade CIN were treated with LLETZ from October 1, 1992 to December 31, 1994. Fifty-three patients (24.4%) had incomplete excision on histology. All patients were followed up cytologically every 3 to 6 months during the first 18 months and then yearly till December 1996. Those patients with positive endocervical margins were followed up with both cervical smear and endocervical smear. RESULTS: The mean follow-up duration was 30.4 months. Ten patients were found to have persistent or recurrent disease. Five patients had second LLETZ and complete excision was achieved in 4 of them, one patient had cone biopsy and two had hysterectomy. One patient was found to have stage I a cervical cancer. CONCLUSION: A report of incomplete excision of CIN after LLETZ calls for follow-up with cytology and colposcopy and not aggressive retreatment.

Adult↗