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Biomedical subjects

A K Tan

Publications and source records attributed to A K Tan.

At least 19 recordsLinked to original sources
PubMed2001

Current and emerging treatments in Parkinson's disease.

INTRODUCTION: Parkinson's disease is one of the commonest neurodegenerative diseases of the elderly. The discovery of dopamine deficiency from the degeneration of substantia nigra neurons revolutionised treatment in the early 70's. METHOD: This review is based on Medline search with Keywords (Parkinson's disease, treatment, therapy, surgery). RESULTS: Levodopa remains the gold standard of medications. New drugs include recently introduced dopamine agonists like ropinorole and pramipexole, and COMT inhibitors. The role of selegiline in neuroprotection remains controversial. Dopamine agonist monotherapy may delay the onset of motor fluctuations. Levodopa may be associated with the earlier onset of motor complications such as dyskinesias, and it may be preferable to delay its use in younger patients. In older patients, especially those with significant disability, levodopa use should not be delayed. Surgical therapies such as pallidotomy, bilateral subthalamic deep brain stimulation and foetal transplantation can be considered for those who fail medical therapy. Molecular science techniques including gene therapy, neurotrophic factors, stem cell technology form the next frontier of Parkinson's research. CONCLUSION: No new medication has proven more efficacious than levodopa. More controlled trials are required in Parkinson's surgery to reach definite conclusions about its effects and long-term results.

Age Factors↗
PubMed1999

Juvenile nasopharyngeal angiofibroma.

This is a retrospective study of 17 patients with juvenile nasopharyngeal angiofibroma treated from 1983 to 1996. Patients with Stage I or II disease according to the Fisch classification system were treated surgically by a transpalatal approach. One patient underwent a Le Fort I osteotomy and down-fracture approach for access. Three patients underwent combined transpalatal and lateral rhinotomy for access, whereas one underwent a transcervical double mandibular osteotomy to facilitate the exposure. A patient with Stage IV disease underwent a combined subcranial frontonasal osteotomy plus a Le Fort I osteotomy for access to a massive angiofibroma. Initial surgical management prevented recurrence in 79% of patients. Two patients with intracranial extension were treated with primary irradiation therapy; their tumours became asymptomatic. Preoperative angiography and embolization were used to treat all surgical candidates. The use of newer craniofacial or subcranial techniques and infratemporal fossa approaches with osteotomies can provide access to large angiofibromas even when there is skull base or intracranial involvement. Surgical exposure may also be enhanced by the use of the Le Fort I osteotomy and down-fracture approaches.

Adolescent↗
PubMed1999

Screening of high-risk infants using distortion product otoacoustic emissions.

Otoacoustic emissions have been used as an objective and noninvasive test of cochlear function. Due to its ease of use, accuracy, and test-retest reliability, otoacoustic emissions testing is considered an excellent tool for evaluating difficult-to-test patients. This project involved screening infants at high risk of congenital hearing loss. These infants were selected from the Special Infant Clinic at Queen's University, Kingston, Ontario. The first part of this project was to establish a distortion product otoacoustic emissions (DPOAEs) "norm" as the reference for this group of patients. A prospective study was then conducted to compare DPOAE and auditory brainstem response (ABR) as screening tools for this group of patients. Auditory brainstem response has been the gold standard for evaluating the hearing status of these infants. We will also present our experience in testing over 50 patients at high risk of congenital hearing loss using DPOAEs.

Audiometry, Evoked Response↗
PubMed1999

The neurological manifestations of Nipah virus encephalitis, a novel paramyxovirus.

A novel Hendra-like paramyxovirus named Nipah virus (NiV) was the cause of an outbreak among workers from one abattoir who had contact with pigs. Two patients had only respiratory symptoms, while 9 patients had encephalitis, 7 of whom are described in this report. Neurological involvement was diverse and multifocal, including aseptic meningitis, diffuse encephalitis, and focal brainstem involvement. Cerebellar signs were relatively common. Magnetic resonance imaging scans of the brain showed scattered lesions. IgM antibodies against Hendra virus (HeV) were present in the serum of all patients. Two patients recovered completely. Five had residual deficits 8 weeks later.

Adult↗
PubMed1999

Palatal myoclonus--a case report.

Palatal myoclonus is usually due to a brainstem or cerebellar lesion disrupting the dentato-rubro-olivary pathway. Rarely it may be caused by a cortical lesion. The precipitating factor in 70% of all cases is an infarct. We describe an unusual case of a patient with palatal myoclonus who had an old ipsilateral cerebellar infarct and a new contralateral subcortical (corona radiata) infarct. We postulate that the new infarct caused disinhibition of the old cerebellar infarct, resulting in palatal myoclonus. Magnetic resonance imaging (MRI) of the brain did not show any hypertrophy of the inferior olivary nucleus. Her myoclonus proved refractory to clonazepam, valproate and phenytoin.

Aged↗
PubMed1999

Fetal scarless wound healing.

Advances in fetal monitoring and open fetal surgery for life-threatening congenital diseases have provided us with the unique opportunity to examine fetal surgical wound healing. Fetal wounds heal rapidly and without scarring. The exact mechanisms of fetal scarless healing remain unknown. This article illustrates the most current understanding of the fetal wound healing process by examining the intrinsic properties of fetal skin, fetal fibroblasts, wound matrix, fetal environment, and various cytokines. In fetal wound, transforming growth factor-beta and hyaluronic acid-rich wound matrix play pivoting roles in scarless repair. Different experimental strategies to manipulate the healing of adult wounds will be presented. These therapeutic measures are based on the scarless fetal wound repair model. We will also briefly comment on the current status of fetal surgery.

Animals↗
PubMed1998

Paroxysmal kinesigenic choreoathetosis in Singapore and its relationship to epilepsy.

OBJECTIVES: To study the clinical characteristics of paroxysmal kinesigenic choreoathetosis (PKC) in our local population and its relationship to epilepsy. METHODS: We reviewed retrospectively 15 patients who were managed by neurologists in our department from 1982 to 1996. The literature was also reviewed to study the association between PKC and epilepsy. RESULTS: In our study, all the cases were idiopathic. The male to female ratio was 14:1 with all major races represented. Sixty percent of our patients suffered dystonic posturing rather than chorea, during the attacks. Twenty-one percent had a family history of a similar disorder which appeared to be of autosomal dominant inheritance. The sporadic form (79%) predominated in Singapore. One had a history of febrile fits while two had a history of epilepsy. We reviewed the available literature and found five other patients with idiopathic PKC also suffering from epilepsy. Of the 83 patients reviewed, 8% had epilepsy. This further strengthens the relationship between the two conditions. All our patients responded well to phenytoin at doses between 100 and 400 mg/day. CONCLUSION: PKC affected all three major races in our population with a high male to female ratio of 14:1. Seventy-nine percent of our cases were sporadic and 60% suffered dystonic posturing during attacks. Of the cases reviewed, 8% of patients with idiopathic PKC also had epilepsy.

Adolescent↗
PubMed1998

Stereotactic microelectrode-guided posteroventral pallidotomy and pallidal deep brain stimulation for Parkinson's disease.

Three patients underwent stereotactic posteroventral pallidotomy, and 1 patient underwent pallidal deep brain stimulation, for medically intractable symptoms of advanced Parkinson's disease, characterized by peak-dose levodopa dyskinesias, wearing-off fluctuations, tremor, rigidity and bradykinesia. Surgery was performed stereotactically under local anaesthesia, with eventual target coordinates derived from a combination of magnetic resonance imaging (MRI), coregistration with an electronic brain atlas, intraoperative microelectrode neuronal recordings and microstimulation before lesioning or placement of a deep brain stimulator was done. Assessment was made at baseline preoperatively and at 3-month intervals postoperatively, with Unified Parkinson's Disease Rating Scale (UPDRS) and Core Assessment Program for Intracerebral Transplantation (CAPIT) scoring. All patients improved in dyskinesia, tremor, rigidity and bradykinesia contralateral to the lesion side, but also on the ipsilateral side to a lesser extent. The improvement was largely seen in the 'off' state: UPDRS by 41%, and CAPIT by 19% on the contralateral side. 'On' freezing was not helped. There were no deaths and no visual complications, but there was one complication of a delayed contralateral upper limb dystonia after pallidotomy. The 1 patient with pallidal deep brain stimulation (DBS) obtained similar improvement as those with pallidotomy. Posteroventral pallidotomy and pallidal stimulation improves all the cardinal features of Parkinson's disease, and effectively ameliorates levodopa dyskinesias.

Electric Stimulation Therapy↗
PubMed1998

The profile of hospitalised patients with Parkinson's disease.

The objective of this study was to provide a profile of patients with Parkinson's disease (PD) who required admission to hospital. We reviewed retrospectively all patients with PD who were admitted to our hospital in 1995. In our study, there were 260 admissions involving 173 PD patients. The average age was 74.7 years. Of these patients, 93 were males and 80 were females. There were 150 Chinese, 12 Indians, 9 Malays, and 2 of other races. The average duration of hospitalisation was 11.7 days. The main reasons for admissions were: 1) chest infections (22%), 2) falls (13%), 3) control of PD symptoms (10%), 4) general medical problems (9%) and 5) urinary dysfunction (8%). Nine per cent were classified as Hoehn and Yahr stage 2, 31% as stage 3, 31% as stage 4 and 24% as stage 5. Twenty-one per cent of our patients were first diagnosed with PD during their hospitalisation. Upon discharge, 26% required transfer to either a community hospital or nursing home. The current in-patient load of PD patients is expected to rise with the ageing population. A significant number of people within the community may have undiagnosed PD. These patients suffer multiple medical problems and need a multi-disciplinary team approach to management. Greater resources will be required to support these patients in the community.

Aged↗
PubMed1998

Creutzfeldt-Jakob disease presenting with visual blurring, diplopia and visual loss: Heidenhain's variant.

Focal electroencephalographic abnormalities as described in Heidenhain's variant of Creutzfeldt-Jakob disease are uncommon. We report a 73-year-old male presenting with visual symptoms, right hemianopia and rapidly progressive dementia. Myoclonus was synchronous with generalised periodic epileptiform discharges on electroencephalography (EEG). In addition, there were periodic focal sharp waves at the left occipital region. Diffusion-weighted magnetic resonance brain images showed slightly increased signal intensity in the occipital parasagittal area, left more than right. 14-3-3 protein was detected in the cerebrospinal fluid. The patient died within 5 months of presentation.

Aged↗
PubMed1998

Botulinum toxin for neurological disorders in a movement disorders clinic in Singapore.

AIM OF STUDY: This study was done to examine the usefulness of botulinum toxin A injections in treating various neurological disorders such as hemifacial spasm, blepharospasm, focal dystonia and task-specific dystonia. METHODS: This was a prospective, open-labelled trial of patients seen in a Movement Disorders Clinic with dyskinesias potentially treatable with botulinum toxin. All patients were assessed before and after injections using clinical rating scales, and those with focal and task-specific dystonias were also recorded on videotape. RESULTS: There were 102 patients with hemifacial spasm, 3 with blepharospasm, 13 with neck dystonia, 6 with writer's cramp, I with musician's cramp, and I with jaw dystonia. All patients with hemifacial spasm and blepharospasm obtained good results, while 77% of those with cervical dystonia received substantial benefit. Only half of those with writer's cramp improved. Hemifacial spasm seems more prevalent in Singapore compared with Western populations. CONCLUSION: Injections of botulinum toxin are useful in treating the various neurological disorders studied. This is an advancement in the treatment of these dyskinesias which respond poorly to oral medications.

Adult↗
PubMed1997

Otolaryngology Web site.

PURPOSE: This article describes the medical Web site developed at the Department of Otolaryngology, Queen's University, on the World Wide Web. The objectives of the Web site are: to introduce the Department of Otolaryngology at Queen's University; to provide it's users with information and new developments in various aspects of otolaryngology; to provide general public with health information on otolaryngology; and to foster academic discussion via electronic discussion forum. The development and implementation of this Web site are also presented. CONCLUSION: Physicians who have Internet access will be able to utilize the multimedia information on this site for medical education and clinical consultation.

Computer Communication Networks↗
PubMed1997

Cosmetic upper-facial rejuvenation with botulinum.

OBJECTIVE: This study was conducted to evaluate the cosmetic use of botulinum toxin type A (Botox), which blocks the release of acetylcholine at the presynaptic neuromuscular junction leading to an irreversible, but temporary chemical denervation muscular paralysis and weakness. This produces a significant cosmetic improvement of wrinkling in the upper face due to hyperfunctional animation. METHOD: A prospective clinical study representing our experience with this new technique is presented. Patient selection and evaluation, classification of animation lines, techniques, results and complications are discussed. In a 15-month period, 23 patients with seven anatomic sites were injected. Twenty-three patients had the lateral aspect and the inferior aspect of their squint lines injected, and 26 patients had their glabellar frownlines injected. RESULTS: Significant improvement occurred to the average depth and length of the glabellar frownlines. The subjective improvement by the patients was also significant. Regarding the crow's feet, the lateral canthal lines showed more improvement than the inferior lateral canthal lines because the latter has a greater component of zygomaticus major and minor muscle, which contributes to the inferior lateral squint line. CONCLUSION: Botox is a safe, easy-to-use, effective modality for the temporary elimination of hyperfunctioning upper-facial muscles.

Botulinum Toxins, Type A↗
PubMed1997

Facial rejuvenation with botulinum.

Botulinum toxin type A (Botox) blocks the release of neurotransmitter acetylcholine at the presynaptic neuromuscular junction leading to an irreversible, but temporary muscular paralysis and weakness. This can produce a significant improvement of wrinkling in the upper face caused by the actions of the facial muscles. A prospective clinical study representing a 15-month experience with this new technique is presented. Patient selection and evaluation, classification of animation lines, techniques, results, and complications are discussed.

Botulinum Toxins, Type A↗
PubMed1996

The syndrome of painful legs and moving toes--a case report.

The syndrome of painful legs and moving toes is an uncommon and distressing condition with pain in the feet or legs and involuntary movements of the toes. It can follow spinal cord or cauda equina trauma, lumbar radiculopathy, injury to the feet, peripheral neuropathy or without any preceding causes. Ephaptic transmission in damaged nerve roots or peripheral nerves with central reorganisation may be the underlying mechanism of the syndrome. Treatment is difficult. We report a case of this syndrome following peripheral neuropathy, with a good early response to the GABA agonists baclofen and clonazepam. The role of different GABA agonists in the treatment of this condition needs to be better defined.

Baclofen↗
PubMed1995

Activation and characterization of procarboxypeptidase B from human plasma.

Recently we reported the isolation and cloning of a novel plasma procarboxypeptidase B that binds plasminogen [Eaton, D. L., Malloy, B. E., Tsai, S. P., Henzel, W., & Drayna, D. (1991) J. Biol. Chem. 266, 21833-21838]. This plasma procarboxypeptidase is structurally similar to tissue procarboxypeptidases, and initial substrate studies showed that this plasma protein behaves like a basic carboxypeptidase and is now known as human plasma procarboxypeptidase B (pro-pCPB). However, unlike the tissue procarboxypeptidases, pro-pCPB is extremely unstable to trypsin activation. Trypsin cleaves pro-pCPB at two sites: Arg-92 and Arg-330. Cleavage at Arg-92 releases the activation peptide and generates an active enzyme. However, cleavage at Arg-330 inactivates pCPB. This renders the characterization of pCPB difficult. We have found that 6-amino-n-hexanoic acid (epsilon ACA), a compeptitive inhibitor of basic carboxypeptidases, selectively limits trypsin cleavage of pro-pCPB. In the presence of epsilon ACA, trypsin cleavage at Arg-330 is significantly limited while the cleavage at Arg-92 is unaffected. Using this approach, active pCPB can now be obtained. Kinetic characterization shows that pCPB behaves like other known basic carboxypeptidases. pCPB is more specific for substrates with C-terminal arginine than those with C-terminal lysine for all the natural and synthetic peptides tested. It also hydrolyzes the synthetic ester substrate more efficiently than the synthetic peptide substrate, especially at high pH. The active site Zn2+ can be replaced with other metals with change in substrate specificity.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗