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Biomedical subjects

L L Chan

Publications and source records attributed to L L Chan.

At least 19 recordsLinked to original sources
PubMed2006

Transcranial magnetic stimulation screening for cord compression in cervical spondylosis.

OBJECTIVE: Cervical spondylosis (CS) often results in various degrees of cord compression, which can be evaluated functionally with transcranial magnetic stimulation (TMS). We investigate the use of TMS as a screening tool for myelopathy in CS. METHODS: We prospectively studied 231 patients classified into Groups 1 to 4 based on MRI grading of severity of cord compromise. TMS elicited central motor conduction times and motor evoked potential (MEP) amplitudes in all 4 limbs. The results were compared with those from 45 healthy controls. RESULTS: TMS showed 98% sensitivity and 98% specificity for cord abnormality using MRI as reference standard. CONCLUSIONS: MEP abnormalities are useful for electrophysiological evaluation of cord compression in CS. While TMS is not a substitute for MRI, it is of value as a rapid, inexpensive and non-invasive technique for screening patients before MRI studies.

Adult↗
PubMed2006

Magnetic resonance imaging of Asians with multiple sclerosis was similar to that of the West.

Magnetic resonance imaging (MRI) of the brain is the most important paraclinical diagnostic test in multiple sclerosis (MS). The appearance of MRI in Asians with MS is not well defined. We retrospectively surveyed the first brain and spinal cord MRI in patients diagnosed to have MS, according to Poser's criteria in seven regions throughout Asia to define the MRI changes among Asians with MS. There were 101 patients with first brain, and 86 with first spinal cord MRI, 66 of whom had both. The brain MRI showed a mean of 17 lesions per patient in T2 weighted images, mostly asymptomatic. Almost all the lesions were in the white matter, particularly in the juxtacortical, deep and periventricular white matter. A third of the lesions were greater than 5 mm, 14% enhanced with gadolinium. There were more supratentorial than infratentorial lesions at a ratio of 7.5: 1. Ninety five percent of the spinal cord lesions were in cervical and thoracic regions, 34% enhanced with gadolinium. The lesions extended over a mean of 3.6 +/- 3.3 vertebral bodies in length. Fifty (50%) of the brain and 54 (63%) of the spinal MRI patients had the optic-spinal form of MS. The MRI of the optic-spinal and classical groups of patients were similar in appearance and distribution, except that the optic-spinal MS patients have fewer brain but longer and more severe spinal cord lesions. In conclusion, the brain and spinal cord MRI of Asian patients with MS was similar to that of the West, although, in this study, Asian MS patients had larger spinal cord lesions.

Adult↗
PubMed2006

Exploring the relationship between Parkinson's disease and hemifacial spasm.

Case reports of co-existent Parkinson's disease (PD) and hemifacial spasm (HFS) suggest that there may be a relationship between these conditions. Three of 300 (1%) PD patients presented with HFS compared with 0/300 (0%) controls. The mean age of the three PD patients with HFS was 68.7 +/- 8.0 (60-76) years, with the majority having left-sided HFS. All three patients developed HFS symptoms at around the onset of PD and they were significantly older than the 100 patients with HFS alone (P < 0.05). Our study demonstrated no significant increased risk of HFS amongst the general PD population and hence HFS symptoms are unlikely to be of clinical importance for most PD patients.

Adult↗
PubMed2006

Young onset hemifacial spasm.

INTRODUCTION: Hemifacial spasm (HFS) frequently affects middle aged individuals and the clinical features and etiology have been well reported. However, there is limited data on the exact pathogenesis in young-onset HFS. If age is a major determinant of the etiology or influences the presentation of HFS, there may be clinical differences between the young and elderly HFS patients. OBJECTIVES: We determined the prevalence, clinical and imaging features of young-onset HFS (age of onset or=65 years) HFS patients. METHODS: We examined consecutive patients clinically diagnosed with HFS in a tertiary referral center. The clinical (demographics, clinical presentation, severity of HFS, associated medical conditions and other variables) and imaging findings of young onset patients and old onset patients were tabulated and compared. RESULTS: Amongst 230 consecutive HFS patients, 15 (6.5%) were young-onset HFS and 50 (21.7%) were old-onset HFS. In the young-onset HFS, the mean age of onset of symptoms was 26.5+/-6.5 (6-30) years, with 80% women and 75.0% of young onset HFS having neurovascular compression (NVC) of the root exit zone (REZ) of the facial nerve on the ipsilateral side; 86.7% had initial onset of twitching in the upper eyelids that later progressed to the lower facial muscles. While the prevalence of hypertension, diabetes mellitus and other associated vascular disorders in late onset HFS was higher than in young onset groups, the clinical features and frequency of NVC of the facial REZ between the two groups were similar. CONCLUSIONS: We demonstrated a 6.5% frequency of young-onset HFS in our cohort of HFS and their clinical presentation was similar to the old onset patients. Genetic, anatomic or other unidentified factors may contribute to NVC in young-onset HFS.

Adult↗
PubMed2005

Ventrolateral medullary compression in hypertensive patients with hemifacial spasm.

In a patient-controlled study, the authors demonstrated a significantly higher prevalence of rostral ventrolateral medulla (VLM) compression in hypertensive patients with hemifacial spasm (HFS) compared with age-, sex-, race-, disease duration-, and disease severity-matched normotensive patients with HFS (p = 0.02). Hypertensive HFS patients were more likely to have a greater severity of neurovascular compression at the VLM compared with normotensive HFS patients (p = 0.008). VLM compression is associated with risk of hypertension in this study population.

Adult↗
PubMed2005

Pectoralis major motor evoked potentials in cervical spondylosis.

Myelopathy is a severe complication of cervical spondylosis (CS). We studied 27 consecutive patients with CS referred for evaluation for possible myelopathy using transcranial magnetic stimulation. The findings were compared with those from 20 normal controls. Magnetic resonance imaging was utilized to assess the degree of cord compromise. Central motor conduction time (CMCT) abnormalities showed equivalent diagnostic yield with pectoralis major (PM) recordings, as compared with combined first dorsal interossei and abductor hallucis recordings. Our findings show that CMCT measurement with PM recordings is of value as a diagnostic adjunct in the electrophysiological evaluation of myelopathy in CS.

Adult↗
PubMed2005

Hemidystonia precipitated by acute pontine infarct.

Hemidystonia is frequently due to an underlying structural lesion in the basal ganglia and thalamus. It has been suggested that a preserved corticospinal tract may be required for hemidystonia to manifest. We provide the first report of a patient who presented with rapid-onset hemidystonia precipitated by an acute pontine infarct demonstrated on diffusion-weighted magnetic resonance imaging. Acute dysregulation of pallidal efferents to the pedunculopontine and/or pontine afferents to the thalamus may precipitate hemidystonia.

Adult↗
PubMed2005

Toxicity and detoxification of lipid-derived aldehydes in cultured retinal pigmented epithelial cells.

Age-related macular degeneration (ARMD) is the leading cause of blindness in the developed world and yet its pathogenesis remains poorly understood. Retina has high levels of polyunsaturated fatty acids (PUFAs) and functions under conditions of oxidative stress. To investigate whether peroxidative products of PUFAs induce apoptosis in retinal pigmented epithelial (RPE) cells and possibly contribute to ARMD, human retinal pigmented epithelial cells (ARPE-19) were exposed to micromolar concentrations of H2O2, 4-hydroxynonenal (HNE) and 4-hydroxyhexenal (HHE). A concentration- and time-dependent increase in H2O2-, HNE-, and HHE-induced apoptosis was observed when monitored by quantifying DNA fragmentation as determined by ELISA, flow cytometry, and Hoechst staining. The broad-spectrum inhibitor of apoptosis Z-VAD inhibited apoptosis. Treatment of RPE cells with a thionein peptide prior to exposure to H2O2 or HNE reduced the formation of protein-HNE adducts as well as alteration in mitochondrial membrane potential and apoptosis. Using 3H-HNE, various metabolic pathways to detoxify HNE by ARPE-19 cells were studied. The metabolites were separated by HPLC and characterized by ElectroSpray Ionization-Mass Spectrometry (ESI-MS) and gas chromatography-MS. Three main metabolic routes of HNE detoxification were detected: (1) conjugation with glutathione (GSH) to form GS-HNE, catalyzed by glutathione-S-transferase (GST), (2) reduction of GS-HNE catalyzed by aldose reductase, and (3) oxidation of HNE catalyzed by aldehyde dehydrogenase (ALDH). Preventing HNE formation by a combined strategy of antioxidants, scavenging HNE by thionein peptide, and inhibiting apoptosis by caspase inhibitors may offer a potential therapy to limit retinal degeneration in ARMD.

Aldehydes↗
PubMed2005

Difficulties with prenatal diagnosis of the Walker-Warburg syndrome.

We describe a postnatally diagnosed case of Walker-Warburg syndrome--a form of congenital muscular dystrophy with lissencephaly and eye abnormalities. We reviewed the literature to highlight its clinico-radiological diagnostic features and discuss the difficulties encountered with prenatal diagnosis, especially in cases with no positive family history. An increased awareness of this rare but lethal condition, and a high index of suspicion during routine antenatal ultrasound, could prompt further advanced fetal ultrasonography and magnetic resonance imaging, and aid in timely prenatal diagnosis, management, and counseling.

Adult↗
PubMed2005

Haemophagocytic lymphohistiocytosis in Malaysian children.

OBJECTIVES: To study the clinical presentation, therapy and outcome of children diagnosed with both primary and secondary haemophagocytic lymphohistiocytosis (HLH) at the University of Malaya Medical Centre. METHODS: All patients diagnosed with HLH between 1998 and 2004 were studied. Clinico-pathological data of these patients were prospectively collected and analysed. RESULTS: Thirteen consecutive patients (eight boys) with a median age of 28 months were seen. All patients presented with high-grade unremitting fever and almost all, with hepatosplenomegaly and cytopenias. Neurological manifestations, which ranged from irritability to seizures and coma, were seen in 10 (77%) patients. Other common presenting features include liver dysfunction (46%) and skin rash (38%). All patients were treated using the HLH-94 protocol chemotherapy which consisted of a combination of etoposide, dexamethasone and cyclosporine. Complete response was seen in seven patients while two required bone marrow transplantation and one developed secondary acute myeloid leukaemia. Two patients died before treatment could be commenced. Overall mortality rate in our series was 46%. CONCLUSIONS: Haemophagocytic lymphohistiocytosis is an uncommon disease with a high fatality rate. Due to its protean clinical manifestations, it may be underdiagnosed. Early detection and prompt institution of appropriate therapy is necessary to improve the outcome in affected patients.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2004

Fragile X premutation alleles in SCA, ET, and parkinsonism in an Asian cohort.

Among 367 subjects, the authors analyzed 167 patients with essential tremor, sporadic progressive cerebellar ataxia, multiple-system atrophy, and atypical parkinsonism and 200 healthy control subjects for FMR1 premutation alleles. None of the subjects carried alleles within the premutation range. These findings suggest that in the absence of other supportive clinical or imaging features, the cost-effectiveness of routine fragile X tremor/ataxia syndrome screening in this Asian cohort with movement disorders was low.

Adult↗
PubMed2004

Clinico-radiologic correlation in unilateral and bilateral hemifacial spasm.

INTRODUCTION: Bilateral hemifacial spasm (HFS) is rare. Clinico-radiologic correlates utilizing advanced imaging techniques have not been systematically examined in bilateral HFS. The prevalence of bilateral HFS in an Asian population has not been clarified. OBJECTIVES: We examined the prevalence and clinico-radiologic correlates of bilateral HFS in a clinic-based cohort and compared the clinical characteristics of unilateral HFS patients with and without contralateral neurovascular contact (NVC) in HFS. METHODS: Patients clinically diagnosed with HFS were examined for bilateral symptoms. Imaging analysis involved the utilization of reformatted, multi-planar three-dimensional time-of-flight magnetic resonance angiography (3D-TOF MRA), and constructive interference at steady state (CISS-MR) sequences. The clinical and imaging data was compared between HFS with and without NVC. RESULTS: Amongst 162 consecutive HFS patients, 2 (1.6%) had bilateral symptoms. Both patients had unilateral onset followed by bilateral and asynchronous facial contractions. The contralateral side of the face began to twitch at a mean of 1.5 years later. MRI/A revealed significant NVC of the root exit zone (REZ) of the facial nerve on the ipsilateral side with mild NVC contralaterally. The degree of NVC correlated with the clinical severity of the patients' symptoms. MRI/A analysis of 40 HFS patients with unilateral symptoms demonstrated NVC on the contralateral side in six patients (15%). The mean age and duration of symptoms were not different between HFS patients with and without contralateral NVC. CONCLUSIONS: We demonstrated clinico-radiologic correlation between the clinical severity and the degree of NVC at the REZ of the facial nerve in bilateral HFS. Amongst unilateral HFS, there was no significant difference clinically between those with and without contralateral NVC. The low 1.6% prevalence of bilateral HFS in our Asian cohort was compatible with the rare prevalence in other ethnic populations.

Adult↗
PubMed2004

Systematic correlation of transcranial magnetic stimulation and magnetic resonance imaging in cervical spondylotic myelopathy.

STUDY DESIGN: A prospective study over a 3.5-year period involving transcranial magnetic stimulation and magnetic resonance imaging. OBJECTIVES: To assess the correlation of transcranial magnetic stimulation and magnetic resonance imaging in cervical spondylotic myelopathy qualitatively and statistically. SUMMARY OF BACKGROUND DATA: Cervical spondylotic myelopathy presents with different degrees of cord compression, which can be assessed by magnetic resonance imaging. There are no large studies correlating transcranial magnetic stimulation and magnetic resonance imaging findings in this condition. METHODS: A total of 141 patients with a clinical diagnosis of cervical spondylotic myelopathy were prospectively studied over a 3.5-year period. They were classified into Groups 1 to 4 based on severity of cervical cord changes on magnetic resonance imaging. All had transcranial magnetic stimulation and central motor conduction time measurements within 2 months of the magnetic resonance imaging study. RESULTS: Twenty-eight, 49, 28, and 36 patients were classified into Groups 1 to 4, respectively. Mean upper limb and lower limb central motor conduction times correlated with the severity of magnetic resonance cord compression. The absence of central motor conduction time abnormalities correlated reliably with the absence of cervical cord impingement as in Group 1. Statistically significant right left difference in central motor conduction time in the lower limbs was seen between Groups 1 (no cord changes) and Group 2 (mild cord impingement). Eight other patients with diagnoses other than cervical spondylotic myelopathy all showed central motor conduction time abnormalities. The sensitivity and specificity for transcranial magnetic stimulation for differentiating the presence from absence of magnetic resonance imaging cord abnormality were 100% and 84.8%, respectively. CONCLUSIONS: Transcranial magnetic stimulation showed excellent correlation with magnetic resonance imaging findings and can be considered as an effective technique for screening patients for cervical cord abnormalities before magnetic resonance imaging in the clinical setting. The findings in this study have relevant implications in the pathophysiology, management, and health costs of cervical spondylotic myelopathy.

Adult↗
PubMed2004

Overriding fifth finger: an unusual sign in lower brachial plexopathy.

Hand deformities are often useful clinical signs. To our knowledge, they have not been described in association with brachial plexus lesions. A 28-year-old female presented with sudden left shoulder pain and medial forearm parasthesia. Examination showed the left fifth finger adducting and flexing over the dorsal aspect of the fourth finger. Neurophysiological studies and MRI supported a brachial plexus lesion. The physical sign was not present 5 months post onset and the patient experienced near complete clinical improvement. The unusual physical sign occurred in association with neuralgic amyotrophy. Its occurrence can be explained in terms of transient patchy involvement of nerve fascicles in the brachial plexus.

Adult↗
PubMed2004

Treating childhood acute myeloid leukaemia with the AML-BFM-83 protocol: experience in a developing country.

Treatment for childhood acute myeloid leukaemia (AML) consists of remission induction chemotherapy followed by postremission chemotherapy with or without bone marrow transplantation. The AML Berlin-Frankfurt-Munster (BFM)-83 protocol with induction-consolidation-maintenance chemotherapy for 2 years has been reported to result in a 6-year event-free survival (EFS) and event-free interval (EFI) of 49% and 61% respectively. A total of 174 Malaysian children were treated with this protocol between 1985 and 1999. The 5-year EFS and EFI was 30.7% and 48.0% respectively. The overall mortality from sepsis was 24%, which needs urgent address. The 5-year EFS for patients treated before 1993 and after 1993 was 18.6% and 41.3%, respectively (P = 0.04), while the EFI was 32% and 60.6% respectively (P = 0.034). The improvement seen after 1993 was related to a reduction in induction deaths for that period and probably reflected increased capability and familiarity to cope with the demands of the AML-BFM-83 protocol and accompanying complications in the treatment of AML.

Adolescent↗
PubMed2004

Acute ophthalmoparesis in the anti-GQ1b antibody syndrome: electrophysiological evidence of neuromuscular transmission defect in the orbicularis oculi.

OBJECTIVE: To prospectively study anti-GQ1b antibody positive cases of acute ophthalmoparesis (AO) clinically and electrophysiologically. METHODS: Nine consecutive cases presenting with predominantly acute ophthalmoplegia were assessed clinically and had stimulated single fibre electromyography (SFEMG) of the orbicularis oculi at presentation. All had magnetic resonance imaging brain scans and anti-GQ1b antibody titres determined. RESULTS: Four cases had elevated anti-GQ1b antibody titres and abnormal SFEMG studies, which improved in tandem with clinical recovery over three months. Five other anti-GQ1b antibody negative cases were diagnosed as diabetic related cranial neuropathy, idiopathic cranial neuropathy, ocular myasthenia gravis, and Tolosa-Hunt syndrome. All five cases showed complete recovery over a three month period. CONCLUSIONS: This study demonstrated electrophysiologically the dynamic improvement of neuromuscular transmission of anti-GQ1b antibody positive cases of AO, in tandem with clinical recovery. SFEMG is of value in differentiating weakness due to neuromuscular transmission defect from neuropathy in these clinical situations.

Acute Disease↗
PubMed2004

Monophasic, solitary tumefactive demyelinating lesion: neuroimaging features and neuropathological diagnosis.

The characteristic clinicoradiological findings of multiple sclerosis and acute disseminated encephalomyelitis (ADEM), demonstrating a recurrent progressive course in the former and monophasicity in the latter associated with multiple discrete white matter lesions with variable enhancement on MRI, are not a diagnostic challenge. On the other hand, the less typical radiological presentation of a solitary tumefactive demyelinating lesion mimics a neoplasm, and often necessitates a biopsy. Nonetheless, histopathological examination is an imperfect gold standard and the recognition of certain imaging features may facilitate the correct diagnosis.

Adult↗