PubMed Health⌕ Search

Biomedical subjects

Alan R Cohen

Publications and source records attributed to Alan R Cohen.

At least 19 recordsLinked to original sources
PubMed2006

Cowden disease and Lhermitte-Duclos disease: an update. Case report and review of the literature.

OBJECT: Cowden disease is a rare autosomal-dominant phacomatosis and cancer syndrome that is associated with Lhermitte-Duclos disease (LDD), also called dysplastic cerebellar gangliocytoma. METHODS: In this review the authors summarize the additions to the literature during the past 5 years, with emphasis on new case reports and advances in imaging and molecular biology. Adult-onset LDD is now considered pathognomonic for Cowden disease. Approximately 220 cases of LDD have been reported. Magnetic resonance imaging in patients with LDD is often diagnostic, and imaging studies have facilitated accurate diagnosis and contributed to the improved outcome in affected patients. Cowden disease and other rare, related disorders, such as Bannayan-Riley-Ruvalcaba, Proteus, and Proteus- like syndromes, are often caused by mutations of the PTEN gene. CONCLUSIONS: Because of the high incidence of systemic cancer in patients with Cowden disease, it is important for neurosurgeons to recognize the association between this disease and LDD and to refer affected patients for appropriate cancer screenings and interventions.

Adolescent↗
PubMed2006

New advances in iron chelation therapy.

The emergence of new chelators is likely to have a major impact on the treatment of thalassemia major, sickle cell disease and other hematologic disorders for which regular red cell transfusions are required either to correct severe anemia or to prevent major complications of the underlying disease. In comparison with deferoxamine, which requires prolonged parenteral infusion to achieve negative iron balance, orally active chelators offer the promise of easier administration and better compliance. Moreover, the availability of more than one iron chelator opens up the possibility of combination therapy to target iron in specific organs and to enhance overall iron excretion. Long-term studies, employing new technologies to measure tissue iron, are required to determine whether the new chelators will be as safe and effective as deferoxamine in maintaining control of iron stores and preventing iron-induced cardiac disease, the major complication of transfusional iron overload.

Administration, Oral↗
PubMed2006

Virtual environment-based training simulator for endoscopic third ventriculostomy.

A virtual environment-based endoscopic third ventriculostomy simulator is being developed for training neurosurgeons as a standardized method for evaluating competency. Magnetic resonance (MR) images of a patient's brain are used to construct the geometry model, realistic behavior in the surgical area is simulated by using physical modeling and surgical instrument handling is replicate by a haptic interface. The completion of the proposed virtual training simulator will help the surgeon to practice the techniques repeatedly and effectively, serving as a powerful educational tool.

Computer Simulation↗
PubMed2005

Haploinsufficiency of telomerase reverse transcriptase leads to anticipation in autosomal dominant dyskeratosis congenita.

Dyskeratosis congenita is a rare inherited disorder characterized by abnormal skin manifestations. Morbidity and mortality from this disease is usually due to bone marrow failure, but idiopathic pulmonary fibrosis and an increased cancer predisposition also occur. Families with autosomal dominant dyskeratosis congenita display anticipation and have mutations in the telomerase RNA gene. We identified a three-generation pedigree with autosomal dominant dyskeratosis congenita, anticipation, and telomere shortening. We show that a null mutation in motif D of the reverse transcriptase domain of the protein component of telomerase, hTERT, is associated with this phenotype. This mutation leads to haploinsufficiency of telomerase, and telomere shortening occurs despite the presence of telomerase. This finding emphasizes the importance of telomere maintenance and telomerase dosage for maintaining tissue proliferative capacity and has relevance for understanding mechanisms of age-related changes.

Adolescent↗
PubMed2005

Seasonal variation of pretransfusion hemoglobin levels in patients with thalassemia major.

Patients with thalassemia major often report that they do not maintain their usual pretransfusion hemoglobin concentration during the summer season. We collected 3977 pretransfusion hemoglobin values, amount of blood transfused, and intertransfusion intervals for 94 patients with thalassemia major from 4 centers worldwide. We also assessed the hematocrits of blood donors, the hemoglobin content of units transfused in one center, and the local mean monthly temperatures during the periods of data collection. Pretransfusion hemoglobin levels were significantly lower during the summer in all centers except the one center where monthly temperatures have the least variation throughout the year. A similar relationship to temperature was observed for the hematocrits of blood donors and the hemoglobin content of donor units. This study confirms that pretransfusion hemoglobin levels in patients with thalassemia major are lower in the summertime. Possible mechanisms include expansion of plasma volume with resultant hemodilution in the patient and lower hemoglobin content in donor blood.

Adolescent↗
PubMed2005

1/T2 and magnetic susceptibility measurements in a gerbil cardiac iron overload model.

PURPOSE: To measure the transverse relaxation rate (1/T2) and magnetic susceptibility of the heart in conditions of iron overload by using magnetic resonance (MR) imaging and to correlate these with the tissue iron concentration in a gerbil model. MATERIALS AND METHODS: With prior approval by the institutional animal care and use committee, iron overload was induced with one to 15 weekly subcutaneous injections of iron dextran. Nine gerbils had one to five injections, 10 had six to 10, and eight had 13-15. T2 of the whole heart was measured ex vivo (n=27), and the magnetic susceptibility of the tissue was estimated through measurement of the tissue lysate (n=25). The iron level was measured (in milligrams of iron per gram of wet tissue) with chemical analysis after MR imaging. While 1/T2 and magnetic susceptibility are not equivalent measures of the chemically determined tissue iron level, correlations were expected and were identified by using linear regression models. RESULTS: Iron concentration range was 0.28-1.95 mg/g wet tissue. Iron concentration was strongly correlated with 1/T2 (r=0.92, P <.001, and the root of the mean squares error of the linear prediction, epsilonRMS, was 0.17 mg Fe/g wet tissue with a repetition time of 700 msec). Iron concentration also was strongly correlated with magnetic susceptibility (r=0.90, P <.001, epsilonRMS=0.19 mg Fe/g wet tissue). Multiple regression analysis with combined 1/T2 (with repetition time of 700 msec) and magnetic susceptibility data led to a slight increase in r and decrease in epsilon(RMS) (r=0.93, P <.001, epsilonRMS=0.16 mg Fe/g wet tissue). CONCLUSION: The results of this animal model study demonstrate that 1/T2 and magnetic susceptibility values can be used for estimation of the iron level in the heart.

Animals↗
PubMed2005

Pineal region giant cell astrocytoma associated with tuberous sclerosis: case report.

Tuberous sclerosis complex is a genetic disorder characterized by the development of hamartomas in multiple organs including the brain, skin, eye, kidney, and heart. Neurological features include seizures and mental retardation. Cortical tubers and subependymal nodules are the characteristic intracranial lesions of tuberous sclerosis. Subependymal giant cell astrocytomas, typically located adjacent to the foramen of Monro, can enlarge and cause symptomatic ventricular obstruction. The authors describe the case of a 3-year-old boy with a history of tuberous sclerosis and retinal lesions who presented with an enlarging enhancing pineal region mass. Via an infratentorial supracerebellar approach, the mass was removed using both the operative microscope and a rigid neuroendoscope. Pathological examination showed a giant cell astrocytoma. To the authors' knowledge, this is the first reported case of tuberous sclerosis associated with a giant cell astrocytoma of the pineal region. Diagnostic considerations are discussed.

Astrocytoma↗
PubMed2004

Complications of beta-thalassemia major in North America.

Treatment of patients with beta-thalassemia major has improved dramatically during the past 40 years; however, the current clinical status of these patients remains poorly characterized. We performed a cross-sectional study of 342 patients in the Registry of the National Institutes of Health-sponsored Thalassemia Clinical Research Network. Evidence of hepatitis C exposure was present in 35% of tested patients, was associated with age, and had a rate of spontaneous viral clearance of 33%. Ferritin levels ranged from 147 to 11 010 ng/mL (median, 1696 ng/mL). Median hepatic iron content was 7.8 mg/g dry weight and 23% of patients had values of 15 mg/g dry weight or higher. No patients 15 years or younger and 5% of patients aged 16 to 24 years had heart disease requiring medication. Ten percent had cirrhosis on biopsy. Endocrinologic complications were common among adults. Seventy-four (22%) patients had recent implantable central venous access devices (CVADs) placed. Among 80 episodes of bacteremia in 38 patients, 90% were attributable to the CVAD. Among 330 patients who had received deferoxamine chelation therapy, 224 (68%) reported no complications. We conclude that hepatitis C, iron-related organ dysfunction, and complications of iron chelation therapy are strongly age-dependent in North American patients with beta-thalassemia.

Adolescent↗
PubMed2004

MRI measurement of hepatic magnetic susceptibility-phantom validation and normal subject studies.

A magnetic resonance (MR) imaging method with the potential for assessing hepatic iron overload from measurements of hepatic magnetic susceptibility in vivo is described. Using the blood in the portal and hepatic veins as an internal reference, this technique uses the orientation dependence of signal phase to measure the susceptibility of the liver parenchyma. Computer simulations were done to investigate the requirements on spatial resolution and contrast ratio between the vessels and the background liver tissue for data acquisition. Validation studies were conducted using tube-embedded gel phantoms doped with iron-dextran from 0 to 10 mg Fe/mL to mimic healthy and iron-overloaded livers. The phantom measurements were conducted without motion and flow, under respiration-like oscillatory motion, and with flow. Studies on six normal human subjects demonstrated excellent reproducibility and precision. All images were collected at 1.5 T using a 3D T(1)-weighted turbo field echo sequence for inflow MR angiographies with full flow compensation and capable of cardiac synchronization, navigator gating, and motion correction.

Algorithms↗
PubMed2004

Iron chelation therapy in sickle-cell disease and other transfusion-dependent anemias.

Regular red cell transfusion therapy may be life-saving or may reduce complications substantially in several hematological disorders. The inevitable consequence of repeated transfusions is iron loading, which, if untreated, leads to organ failure and death. Chelation therapy with deferoxamine is the standard of care for patients who have transfusional iron overload. The necessity to administer this drug parenterally limits compliance; this has prompted the search for a safe and effective orally-administered chelator. Deferiprone, the first extensively studied orally active chelator, is now licensed for use in Europe for patients who are unable to use deferoxamine effectively or safely. ICL670, a newer oral chelator, is being tested in large clinical trials. Combined therapies, potentially including transfusional methods to reduce iron loading with parenteral and oral chelators, may improve compliance and efficacy in some patients who are transfused chronically.

Anemia↗
PubMed2004

Positive heterophile antibody test and massive splenomegaly in an adolescent with previously unsuspected Gaucher disease.

Mild splenomegaly is common in patients with Epstein-Barr virus-associated infectious mononucleosis. Massive splenomegaly, however, is rare and requires further evaluation to exclude other causes. We report an adolescent girl with previously undiagnosed type 1 Gaucher disease who presented with massive splenomegaly. The diagnosis of her underlying condition was hampered by the presence of a positive heterophile antibody test for infectious mononucleosis.

Adolescent↗
PubMed2004

Thalassemia.

New developments in the epidemiology, treatment and prognosis of thalassemia have dramatically altered the approach to the care of affected patients, and these developments are likely to have an even greater impact in the next few years. Demographic changes have required an awareness and understanding of the unique features of thalassemia disorders that were previously uncommon in North America but are now seen more frequently in children and recognized more consistently in adults. New methods for measuring tissue iron accumulation and new drugs to remove excessive iron are advancing two of the most challenging areas in the management of thalassemia as well as other transfusion-dependent disorders. Improved survival of patients with thalassemia has given new importance to adult complications such as endocrinopathies and hepatitis that have a major impact on the quality of life. This chapter describes how these changes are redefining the clinical management of thalassemia. In Section I, Dr. Renzo Galanello describes recent advances in iron chelation therapy. Several new chelators are either licensed in some countries, are in clinical trials or are in the late stages of preclinical development. Some of these iron chelators, such as deferiprone (DFP) and ICL670, are orally active. Others, such as hydroxybenzyl-ethylenediamine-diacetic acid (HBED) and starch deferoxamine, require parenteral administration but may be effective with less frequent administration than is currently required for deferoxamine. Chelation therapy employing two chelators offers the possibility of more effective removal of iron without compromising safety or compliance. Other strategies for chelation therapy may take advantage of the ability of particular chelators to remove iron from specific target organs such as the heart and the liver. In Section II, Dr. Dudley Pennell addresses cardiac iron overload, the most frequent cause of death from chronic transfusion therapy. The cardiac complications related to excessive iron may result from long-term iron deposition in vulnerable areas or may be due to the more immediate effects of nontransferrin-bound iron. Cardiac disease is reversible in some patients with intensive iron chelation therapy, but identification of cardiac problems prior to the onset of serious arrhythmias or congestive heart failure has proven difficult. New methods using magnetic resonance imaging (MRI) have recently been developed to assess cardiac iron loading, and studies suggest a clinically useful relationship between the results using these techniques and critical measures of cardiac function. Measurements such as T2* may help guide chelation therapy in individual patients and may also enhance the assessment of new chelators in clinical trials. The use of MRI-based technology also holds promise for wider application of non-invasive assessment of cardiac iron in the management of patients with thalassemia. In Section III, Dr. Melody Cunningham describes some of the important complications of thalassemia that are emerging as patients survive into adulthood. Hepatitis C infection is present in the majority of patients older than 25 years. However, antiviral therapy in patients with thalassemia has been held back by the absence of large clinical trials and concern about ribavirin-induced hemolysis. More aggressive approaches to the treatment of hepatitis C may be particularly valuable because of the additive risks for cirrhosis and hepatocellular carcinoma that are posed by infection and iron overload. Thrombosis is recognized with increasing frequency as a significant complication of thalassemia major and thalassemia intermedia, and pulmonary hypertension is now the focus of intense study. Risk factors for thrombosis such as splenectomy are being identified and new approaches to anticoagulation are being initiated. Pregnancies in women with thalassemia are increasingly common with and without hormonal therapy, and require a better understanding of the risks of iron overload and cardiac disease in the mother and exposure of the fetus to iron chelators. In Section IV, Dr. Elliott Vichinsky describes the dramatic changes in the epidemiology of thalassemia in North America. Hemoglobin E-beta thalassemia is seen with increasing frequency and poses a particular challenge because of the wide variability in clinical severity. Some affected patients may require little or no intervention, while others need chronic transfusion therapy and may be appropriate candidates for hematopoietic stem cell transplantation. Enhancers of fetal hemoglobin production may have a unique role in Hb E-beta thalassemia since a modest increase in hemoglobin level may confer substantial clinical benefits. Alpha thalassemia is also being recognized with increasing frequency in North America, and newborn screening for Hemoglobin Barts in some states is leading to early detection of Hb H disease and Hb H Constant Spring. New data clarify the importance of distinguishing these two disorders because of the increased severity associated with Hb H Constant Spring. The use of intrauterine transfusions to sustain the viability of fetuses with homozygous alpha thalassemia has created a new population of patients with severe thalassemia and has raised new and complex issues in genetic counseling for parents with alpha thalassemia trait.

Heart↗
PubMed2003

Safety and effectiveness of long-term therapy with the oral iron chelator deferiprone.

The identification of a safe, orally active iron chelator is critically important for the prevention of morbidity and early death in patients receiving regular red cell transfusions. Based on our findings in a 1-year multicenter, prospective study of the safety and efficacy of deferiprone in patients with thalassemia major, we have extended the treatment period to 4 years. The mean dose of the chelator was 73 mg/kg per day during 531 patient-years. The rates of agranulocytosis (absolute neutrophil count [ANC] < 500 x 10(9)/L) and milder forms of neutropenia (ANC, 500-1500 x 10(9)/L) were 0.2 and 2.8 per 100 patient-years, respectively. Neutropenia occurred significantly more commonly in patients with intact spleens. Gastrointestinal and joint symptoms decreased significantly after the first year of therapy, and led to discontinuation of deferiprone in only one patient in years 2 to 4. The mean alanine aminotransferase (ALT) value of 71 U/L after 4 years of therapy was significantly higher than the baseline value of 61 U/L. Trend analysis showed no increase in the ALT levels or the percentage of patients with ALT levels greater than twice the upper limit of the reference range. Ferritin levels did not change significantly from the values at the time of change from deferoxamine to deferiprone in either the intention-to-treat analysis or in the 84 patients who completed 4 years of therapy. Because of concerns regarding the effectiveness of the studied dose of deferiprone, 47 patients discontinued therapy, whereas 15 patients interrupted therapy because of concerns regarding low iron levels. The results of this study help to define the safety and effectiveness of long-term therapy with deferiprone.

Administration, Oral↗
PubMed2003

Self-reported initial management of childhood idiopathic thrombocytopenic purpura: results of a survey of members of the American Society of Pediatric Hematology/Oncology, 2001.

The purpose of this study was to update physicians' self-reported initial management practices for childhood idiopathic thrombocytopenic purpura (ITP) from an initial survey in 1997. A questionnaire was sent by e-mail in October 2001 to 753 members of the American Society of Pediatric Hematology/Oncology (ASPH/O). The questionnaire had 14 questions, based on the clinical presentation of a 5-year-old boy with ITP, a platelet count of 7,000/microL, scattered petechiae, and no mucous membrane bleeding. Two hundred eighteen (29%) surveys were returned. In response to questions regarding initial treatment, 33% of physicians said they would always administer drug therapy, 38% usually, 15% sometimes, and 14% rarely/never. When asked which agent would be used if drug treatment were prescribed, 45% reported anti-D, 33% IVIG, 20% prednisone, and 2% other regimens. Only 34% of physicians would always or usually hospitalize such a patient. Hospitalization was more likely if a physician responded that he or she would always or usually use drug therapy. Physicians who saw more ITP patients were more likely to self-report sometimes or rarely/never prescribing drug therapy. Self-reported initial management of ITP by ASPH/O members in 2001 is similar to 1997 regarding the percentage of pediatric hematologists who would not use drug therapy. Among physicians who would use drug treatment, there was an increased use of anti-D and decreased use of IVIG and prednisone. This information provides the basis for designing a randomized clinical trial to compare the effect of different management strategies on the outcomes of bleeding symptoms, side effects of therapy, costs, and quality of life.

Adult↗
PubMed2002

Lack of progressive hepatic fibrosis during long-term therapy with deferiprone in subjects with transfusion-dependent beta-thalassemia.

Patients with thalassemia major require lifelong chelation therapy to prevent iron-induced organ damage. The orally active chelator deferiprone has been proposed as an alternative for patients unable or unwilling to use deferoxamine. One report has concluded that deferiprone may worsen hepatic fibrosis in patients with thalassemia, whereas others have found no detrimental effect. A panel of 3 pathologists evaluated 112 coded liver biopsies obtained from 56 patients before and after deferiprone therapy. Fibrosis was scored with the Laennec and Ishak systems. The mean interval between liver biopsies was 3.1 years (range, 1.2-4.9 years). In 11 patients seronegative for hepatitis C, fibrosis scores before and after therapy were 1.12 +/- 1.07 and 0.97 +/- 0.84 (P =.42) with the use of the Ishak system, and 0.71 +/- 0.65 and 0.70 +/- 0.53 (P =.91) with the Laennec system. Among 45 patients seropositive for hepatitis C, fibrosis scores before and after therapy were 1.91 +/- 1.13 and 2.04 +/- 1.30 (P =.43) with the use of the Ishak system and 1.26 +/- 0.73 and 1.35 +/- 0.90 (P =.41) with the Laennec system. When the data set was limited to biopsies that each contained 6 or more portal tracts (31 patients), analysis still showed no significant change in fibrosis with time. With the use of the Laennec system, the fibrosis score did not increase by more than one level in any patients without hepatitis C; it increased by more than one level in 1 patient with hepatitis C; and it did not decrease by more than one level in any of the 56 patients. This analysis of the largest collection of liver biopsies reported to date in patients receiving deferiprone demonstrates no evidence of deferiprone-induced progression of hepatic fibrosis during long-term therapy.

Adolescent↗
PubMed2002

End-stage liver disease in persons with hemophilia and transfusion-associated infections.

Many persons with hemophilia were infected with hepatitis C and B viruses (HCV, HBV) and HIV, but the consequences of these transfusion-acquired infections are poorly defined. We estimated the risk of HCV-related end-stage liver disease (ESLD) and the associations of age, HBV, and HIV with that risk. All 1816 HCV-seropositive hemophilic patients at 16 centers were followed for up to 16 years. Of these, 624 were HIV(-) and 1192 were HIV-coinfected; 135 had persistent HBV surface antigenemia, 1374 had resolved HBV infection, and 287 were HBV-uninfected. ESLD was defined as bleeding esophageal varices, hepatic encephalopathy, persistent ascites, or death excluding nonhepatic causes of these conditions. Competing risk models were used to estimate the annual hazard rate and cumulative incidence of ESLD. Proportional hazards models were used to estimate relative hazards of ESLD with covariates. ESLD developed in 127 of the HCV/HIV-coinfected participants, with an estimated 16-year cumulative incidence of 14.0% (95% confidence interval [CI], 11.6%-16.4%). Without HIV, 10 HCV-infected participants developed ESLD, for a significantly lower cumulative incidence of 2.6% (95% CI, 1.0%-4.3%, P <.0001). ESLD risk increased steeply with age in both groups. With HIV, ESLD risk was increased 8.1-fold (95% CI, 1.9-35.2) with HBV surface antigenemia, 2.1-fold (95% CI, 1.3-3.3) with fewer than 0.2 x 10(9)/L (200/microL) CD4(+) lymphocytes, and 1.04-fold (95% CI, 1.03-1.06) per year of age. Thus, HIV is associated with a markedly increased risk of HCV-related ESLD for persons with hemophilia, particularly with HBV infection, low CD4(+) lymphocytes, or older age.

Adolescent↗
PubMed2002

Evaluation of iron overload by single voxel MRS measurement of liver T2.

PURPOSE: To overcome the difficulty of poor signal-to-noise ratio of magnetic resonance imaging (MRI) in evaluating heavy iron overload by using a single voxel magnetic resonance spectroscopy (MRS) technique. MATERIALS AND METHODS: A single voxel STEAM pulse sequence with a minimum TE of 1.5 msec and a sampling volume of 36.6 cm(3) was developed and applied to 1/T2 measurement of the liver in 14 patients with thalassemia whose liver iron concentration was determined through biopsy. RESULTS: The iron level ranged from 0.23 to 37.15 mg Fe/g dry tissue with a median value of 18.06. In all cases, strong MR signals were obtained. 1/T2 was strongly correlated with the liver iron concentration (r = 0.95, P < 0.00005). CONCLUSION: The single voxel MRS measurement of T2 in liver iron overload overcomes the difficulty of lack of detectable signals in conventional MRI when the iron level is high. There is an excellent correlation between the iron level and 1/T2.

Adolescent↗