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Biomedical subjects

L H Tan

Publications and source records attributed to L H Tan.

33 records · Page 2Linked to original sources
PubMed2000

Rosai-Dorfman disease of the breast: a mimic of breast malignancy.

Rosai-Dorfman disease (RDD) or sinus histiocytosis with massive lymphadenopathy (SHML) is primarily a nodal-based, idiopathic, benign proliferative disorder of histiocytes with 43% of these cases also involving extranodal sites. The breast is an unusual site of occurrence of RDD. We report two cases of this exceptional event. The first represents an intramammary nodal Rosai-Dorfman disease, while the second is an extranodal disease with sole involvement of the breast. In both, the possibility of malignancy was raised. Histological examination of the two breast lesions revealed sheets of characteristic large histiocytes displaying emperipolesis, a microscopic hallmark of this disease. Immunohistochemical and ultrastructural studies were also performed; the former showed cytoplasmic staining of histiocytes for S-100 protein, while histiocytes that engulfed lymphocytes and plasma cells were identified on electron microscopy.

Adult↗
PubMed2000

Phonology matters: the phonological frequency effect in written Chinese.

Does phonology play a role in silent reading? This issue was addressed in Chinese. Phonology effects are less expected in Chinese than in alphabetical languages like English because the basic units of written Chinese (the characters) map directly into units of meaning (morphemes). This linguistic property gave rise to the view that phonology could be bypassed altogether in Chinese. The present study, however, shows that this is not the case. We report two experiments that demonstrate pure phonological frequency effects in processing written Chinese. Characters with a high phonological frequency were processed faster than characters with a low phonological frequency, despite the fact that the characters were matched on orthographic (printed) frequency. The present research points to a universal phonological principle according to which phonological information is routinely activated as a part of word identification. The research further suggests that part of the classic word-frequency effect may be phonological.

Adult↗
PubMed2000

Brain activation in the processing of Chinese characters and words: a functional MRI study.

Functional magnetic resonance imaging was used to identify the neural correlates of Chinese character and word reading. The Chinese stimuli were presented visually, one at a time. Subjects covertly generated a word that was semantically related to each stimulus. Three sorts of Chinese items were used: single characters having precise meanings, single characters having vague meanings, and two-character Chinese words. The results indicated that reading Chinese is characterized by extensive activity of the neural systems, with strong left lateralization of frontal (BAs 9 and 47) and temporal (BA 37) cortices and right lateralization of visual systems (BAs 17-19), parietal lobe (BA 3), and cerebellum. The location of peak activation in the left frontal regions coincided nearly completely both for vague- and precise-meaning characters as well as for two-character words, without dissociation in laterality patterns. In addition, left frontal activations were modulated by the ease of semantic retrieval. The present results constitute a challenge to the deeply ingrained belief that activations in reading single characters are right lateralized, whereas activations in reading two-character words are left lateralized.

Adult↗
PubMed1999

The Internal Medicine Center--an integrated solution for information on internal medicine on the World Wide Web.

The World Wide Web (WWW) has grown from being a resource center for a select group of scientists to a large database of information that is available to both professionals and public. The amount of medical information on the Web has been increasing exponentially and thus, it has become increasingly difficult for anyone to be able to search for a specific quantum of information among this mass. Even in mid 1996, it was noted that the amount of information on internal medicine was growing rapidly. Hence, on 21 March 1997, the Internal Medicine Center (IMC) was created and launched. The IMC is an unique concept and it represents the first time that medical data on the web has been organized into a form that intimately parallels clinical medicine. The rationale behind the creation of the IMC can be summarized in three words: information, speed and convenience. The interface used by this center reflects these goals because overuse of large image files are avoided, hence decreasing the access time and yet keeping the information in an easily comprehensible manner. In conclusion, the IMC serves as a useful tool for the layman as well as the expert because the comprehensive information that it offers can be accessed rapidly and conveniently.

Information Services↗
PubMed1998

Effects of perinatal diazepam exposure on the liver of rats.

Diazepam is routinely used in obstetrics in the treatment of maternal eclampsia or as anesthetic induction during deliveries or cesarean sections. We investigated here the effects of perinatal diazepam treatment on the liver of Sprague Dawley rats. From 15th day of gestation to birth pregnant rats were treated daily in the first experimental group (DZ1) with 2.5 mg DZ/kg b.w., s.c., the second (DZ2) with 5 and the third (DZ3) with 10 mg DZ/kg b.w. After birth respective treatment was continued to the pups till 5th day postnatal. One half of pups from DZ2 and control was sacrificed at 12th day, the other were raised to 120th day and then sacrificed. After fixation in formaldehyde serial paraffin sections were processed with proliferating cell nuclear antigen (PCNA), autofluorescence of lipofuscin and Elastica v. Gieson staining. Livers from 12 day old rats showed increased levels of PCNA marked hepatocytes and lipofuscin containing cells. Livers from 120 day old animals exhibited increased levels of PCNA cells especially with weakly stained nuclei, the number of lipofuscin containing cells were decreased in DZ1 and DZ2 but reached in DZ3 the similar number as control. Statistical analysis showed that quantification of Kupffer cells lacked significance. To conclude livers of 12 day old animals demonstrated a stimulated DNA synthesis and an accumulation of nondegradable residues. Livers from 120 day old rats demonstrated an increase in number of potentially proliferating hepatocytes by increased levels of weakly stained PCNA nuclei. At lower dosage DZ seems to inhibit lipofuscinogenesis, at highest dosage DZ accumulates non-degradable residues. Elastica v. Gieson staining was not suitable to quantify Kupffer cells with certainty.

Animals↗
PubMed1996

Erythropoietin production in rats with post-ischemic acute renal failure.

To study the role of erythropoietin (Epo) in the pathogenesis of anemia in acute renal failure (ARF), organ Epo mRNA was measured by RNase protection assay in rats with ARF induced by a one hour-occlusion of the left renal artery. Hematocrit was significantly decreased two hours, 24 hours and one week after renal artery occlusion. A significant reduction in serum haptoglobin at two hours and an increase in serum LDH at 24 hours indicated that hemolysis was the likely cause of the initial fall in hematocrit. However, despite the reduced hematocrit, serum Epo concentrations were not significantly different from controls, suggesting that the anemia is maintained because of lack of an appropriate Epo response. Right renal Epo mRNA levels were not significantly different in all groups, but Epo mRNA levels in post-ischemic kidneys were 50 to 67% lower than in contralateral kidneys. However, Epo mRNA in the post-ischemic kidney was increased sixfold by acute hemorrhage, a rise comparable to the ninefold increase observed in contralateral kidneys. In ARF rats exposed to 7.5% O2 for four hours, right kidney Epo mRNA increased 200-fold over normoxic levels, to a value similar to sham-operated hypoxic controls. Epo mRNA in the post-ischemic kidney also increased 200-fold, to 50% of the level in the contralateral kidney. Hepatic Epo mRNA levels were elevated to comparable levels in both groups. In this ARF model, mild anemia is associated with relative Epo deficiency. In the post-ischemic kidney, a substantial capacity for Epo production is retained but the sensitivity of the Epo response to blood oxygen availability is significantly reduced.

Acute Kidney Injury↗
PubMed1995

Assessment of competence in technical clinical skills of general practitioners.

Technical clinical procedures constitute an important part of the work of general practitioners. Assessment of competence in the relevant skills is important from the perspective of quality assurance. In this study, the psychometric characteristics of three different methods for assessment of competence in technical clinical skills in general practice were evaluated. A performance-based test (8 stations), a written knowledge test of skills (125 items) and a self-assessment questionnaire (41 items) on technical clinical skills were administered to 49 GPs and 47 trainees in general practice. The mean scores on the performance-based test and the written knowledge test of skills showed no substantial differences between GPs and trainees, whereas the GPs scored higher on the self-assessment questionnaire. While the correlation of the score on the knowledge test of skills with the score on the performance-based test was moderately high, the score on the self-assessment questionnaire showed a rather low correlation with the performance-based test. Although performance-based testing is obviously the best method to assess proficiency in hands-on skills, a written test can serve as a reasonable alternative, particularly for screening and research purposes.

Clinical Competence↗
PubMed1993

Infant mortality statistics do not adequately reflect the impact of short gestation.

OBJECTIVE: To determine the accuracy of National Center for Health Statistics cause-specific infant mortality data. The National Center for Health Statistics compiles these data by applying World Health Organization (WHO) selection rules to death certificate data. The WHO rules arrange medical entities into a hierarchical order and select a single underlying cause of death (ULCD). DESIGN: A comparison was made between ULCD assigned to a cohort of 335 infant death certificates by (1) a neonatologist panel, and (2) application of WHO selection rules by the Florida State Office of Vital Statistics (OVS). RESULTS: Among the 146 infants with birth weights 1500 to 4649 g, agreement between neonatologists and OVS was 88%, while among the 189 infants with birth weights 0 to 1499 g (very low birth weight), agreement was just 41%. Neonatologists selected short gestation as the underlying cause of death for 82% of very low birth weight infant records, vs 25% by OVS. Due to the application of specific WHO selection rules, OVS frequently selected immediate causes of death, such as "cardiac arrest," as the ULCD, even when the medical certifier had indicated short gestation as the ULCD. In vital statistics reports, many of these immediate causes are reported as "other respiratory conditions of newborn," or "all other perinatal conditions." CONCLUSION: WHO ULCD selection rules should be modified to allow short gestation to have a higher priority over immediate causes of infant death.

Birth Weight↗
PubMed1989

Immunogenicity of a low dose recombinant DNA hepatitis B vaccine in healthy adults in Singapore.

The immunogenicity and safety of a standard dose of 10 micrograms of a yeast derived recombinant DNA hepatitis B vaccine (B-Hepavac II) was compared with that of a reduced dose of 5 micrograms in 84 healthy adult volunteers with no previous exposure to hepatitis B. Each subject received either a 10 micrograms or 5 micrograms dose of vaccine intramuscularly at 0, 1 and 6 months. One month after the second injection of vaccine the seroconversion rate in the two groups were 85 and 86 percent respectively. Two months after the third injection 100 percent of participants had sero-converted; 95 percent of the 10 micrograms group and 91 percent of the 5 micrograms group had titres of anti-HBs greater than 10 IU/L. The geometric mean titres (GMT) of anti-HBs levels at 2, 6, 8, and 12 months were 34, 61, 811 and 188 IU/L in the 10 micrograms group and 26, 45, 836 and 304 IU/L in the 5 micrograms group respectively. Adverse effects were mild and transient. The vaccine was safe and immunogenic in the doses given. The reduced dose of 5 micrograms was as effective as the standard 10 micrograms dose.

Adolescent↗
PubMed1989

Evidence of viral replication in HBsAg positive patients with hepatocellular carcinoma: measurement of serum hepatitis B virus deoxyribonucleic acid (HBV-DNA).

Sera from 60 consecutive patients with hepatocellular carcinoma (HCC) diagnosed by either a positive histology or at least two of the following: CT scan, hepatic ultrasound, hepatic angiogram and raised alpha-foetoprotein levels, were studied to determine their Hepatitis B surface antigen (HBsAg) status and the frequency of continuing viral replication. Markers of Hepatitis B virus (HBV) infection were detected using enzyme and radioimmunoassays. Hepatitis B DNA (HBV-DNA) was measured by molecular hybridization using a labelled recombinant HBV-DNA probe. Sera from 30 HBsAg positive 'healthy' carriers were used as controls. Forty-seven (78%) patients were HBsAg positive. Evidence of previous HBV infection was present in 12 of 13 HBsAg negative patients. 30% of HBsAg positive patients were HBeAg positive, 62% were anti-HBe positive and 8% had no 'e' markers. Serum HBV-DNA was present in 21 (45%) HBsAg positive patients: 10 (71%) HBeAg positive patients, 10 (35%) anti-HBe positive patients and 1 (25%) patient without any 'e' markers. Serum HBV-DNA levels were less than 0.6 ng/ml in 16 (76%) patients. HBV-DNA was absent in all HCC patients who were HBsAg negative. The frequency of serum HBV-DNA positivity was higher in 30 patients with HCC when compared with 30 age and sex matched healthy HBsAg positive individuals (57% vs 13% p less than 0.01). A sizeable proportion of HBsAg positive HCC patients have on-going viral replication and this is present in patients who were thought to have stopped replicating (anti-HBe positive patients).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMedDate not supplied

Meningioma presenting as a parapharyngeal tumor: report of a case with fine needle aspiration cytology.

BACKGROUND: Meningiomas rarely extend out of their intracranial confines through skull foramina to present as cervical tumors, where they would be accessible to fine needle aspiration (FNA) and thereby create difficulties in cytodiagnosis by mimicking other, more commonly aspirated head and neck tumors. CASE: A psammomatous meningioma arising intracranially and extending through the jugular foramen presented as a mass at the angle of the jaw clinically. On FNA cytology the diagnosis was suggested, but the cytomorphologic features overlapped with those of more commonly aspirated head and neck tumors, such as acinic cell carcinoma arising primarily in a salivary gland, metastatic papillary thyroid carcinoma and paraganglioma (glomus jugulare tumor). These possibilities had to be excluded through correlation with radiologic and intraoperative findings, which showed a dural-based tumor extending through the jugular foramen to assume a parapharyngeal location. Histology of the final excision specimen confirmed a psammomatous meningioma. CONCLUSION: The possibility of meningioma should be considered in the cytologic differential diagnosis of parapharyngeal tumors, particularly since its cytomorphologic features may mimic those of some of the more commonly encountered and aspirated head and neck tumors.

Adipocytes↗
PubMedDate not supplied

Cushing's syndrome in a patient with a corticotropin-releasing hormone-producing pheochromocytoma.

OBJECTIVE: To present the first case of Cushing's syndrome attributable solely to ectopic production of corticotropin-releasing hormone by a pheochromocytoma. METHODS: We summarize the clinical features and results of laboratory investigations in a patient with symptoms characteristic of Cushing's syndrome. RESULTS: Although Cushing's syndrome is usually caused by ectopic production of adrenocorticotropic hormone (ACTH), our current patient had clinical and biochemical evidence of hypercortisolism in conjunction with "normal" ACTH levels and nonsuppressible serum and urinary cortisol levels on low-dose and high-dose dexamethasone suppression testing. An abdominal computed tomographic scan revealed a 7.7-cm mass in the left adrenal gland. Light microscopic examination and immunohistochemical staining showed a pheochromocytoma with mild cortical hyperplasia. Immunostaining was positive for corticotropin-releasing hormone but negative for ACTH. CONCLUSION: To our knowledge, this is the first case of Cushing's syndrome in a patient with pheochromocytoma caused only by ectopic secretion of corticotropin-releasing hormone without accompanying secretion of ACTH.

Journal Article↗