Power calculation for cohort studies with improved estimation of expected numbers of deaths

Summary This paper focuses on improving the accuracy of sample size calculations for cohort studies by careful calculation of the expected number of deaths in the population, taking into account either prior information or realistic assumptions about variables which may affect the mortality or incidence. Sometimes small changes in the assumptions can dramatically alter the expected numbers and may necessitate modifications in the design of the study. Possible modification include extension of the follow-up time, and recognition that the real strength of the study may lie in the potential for pooling several similar studies. The problem will be discussed with reference to two examples of occupational cohort studies where differing prior information was available.

---

Zusammenfassung Diese Arbeit beschäftigt sich mit der Genauigkeit der Berechnung des Stichprobenumfangs in Kohortenstudien, wenn detaillierte Berechnungen für die erwartete Zahl der Verstorbenen berücksichtigt werden. Dies kann entweder durch die Ausnutzung vorhandener Informationen oder durch realistische Annahmen über die Faktoren, die Mortalität oder Inzidenz beeinflussen, geschehen. Schon kleine Unterschiede in diesen Annahmen kann die erwartete Zahl der Verstorbenen erheblich verändern und es notwendig machen, das Design einer Studie zu verändern. Solche Modifikationen bestehen z.B. in der Verlängerung der Follow-up Zeit der Studie oder in der Einsicht, dass es nötig ist, Daten aus mehreren Studien zusammenzufassen. Die Probleme werden anhand von zwei Beispielen aus dem Bereich der Berufsepidemiologie diskutiert.

---

Résumé Cet article concerne la précision des estimations de taille d'échantillons pour les études de cohortes. Le calcul précis du nombre de décès attendus dans la population prend en compte les variables susceptibles d'affecter la mortalité ou l'incidence, provenant soit d'une connaissance préalable, soit d'hypothèses réalistes. De modestes changements d'hypothèses peuvent parfois altérer de façon substantielle les nombres attendus et nécessiter des modifications dans le protocole de l'étude. Parmi les modifications possibles, il faut citer la prolongation du temps de suivi de l'étude ainsi que le constat que la valeur réelle de l'étude pourrait reposer sur la possibilité de mise en commun de plusieurs études similaires. Le problème est discuté à l'aide de deux exemples d'études de cohortes professionnelles pour lesquelles différentes informations préalables sont disponibles.

     

A comparison of tympanic thermometer readings to pulmonary artery catheter core temperature recordings

The purpose of this study was to determine the accuracy of FirstTemp (Intelligent Medical Systems, Carlsbad, CA) tympanic thermometer readings compared with core body temperatures obtained via pulmonary artery catheter (PAC). Five measurements were obtained on 19 cardiovascular surgery patients. Tympanic thermometer measurements tended to be higher than PAC measurements. However, most of the differences were not clinically significant. Differences found between right and left ear measurements were most likely due to poor measurement technique. When the correct technique is used, nurses can be confident that tympanic temperature readings are clinically accurate.     

Differentiation of a primitive neuroectodermal tumor into a benign ganglioglioma

We describe a case of cerebellar neuroblastoma with histologic documentation of maturation into a ganglioglioma sixteen months later. Only chemotherapy was administered following the initial surgery and the child is well and disease-free three years following her final surgical procedure. The outcome of this patient supports previous hypotheses that the cerebellar neuroblastoma may be a less malignant tumor than its other primitive neuroectodermal posterior fossa counterparts. Furthermore, this case suggests a role for second-look surgery in the management of selected pediatric brain tumors.     

Symptomatic treatment in the fragile X-associated tremor/ataxia syndrome.

There is no established treatment for the neurological features of the recently discovered fragile X-associated tremor/ataxia syndrome (FXTAS). Fifty-six patients with FXTAS completed a questionnaire to determine whether any medications had been effective for neurological symptoms. Of 11 subjects with definite FXTAS, 8 (70%) were on medications for their neurological symptoms, whereas most subjects with possible or probable FXTAS, 31 (70%) of 45 subjects, were not on medications. Although no therapy was uniformly effective for intention tremor, ataxia, Parkinsonism, memory loss, or anxiety, some subjects with intention tremor or Parkinsonism reported improvement with medications frequently used in other movement disorders. Overall, all 22 subjects on medications reported improvement in one or more symptoms. Lack of insight, recall bias, and cognitive impairment may have resulted in an underestimation of the beneficial effect of medical therapy. This study suggests that patients with FXTAS can derive improvement from medication treatment for some of their symptoms.     

Plasticity of human motion processing mechanisms following surgery for infantile esotropia

Monocular oscillatory-motion visual evoked potentials (VEPs) were measured in prospective and retrospective groups of infantile esotropia patients who had been aligned surgically at different ages. A nasalward-temporal response bias that is present prior to surgery was reduced below pre-surgery levels in the prospective group. Patients in the retrospective group who had been aligned before 2 yr of age showed lower levels of response asymmetry than those who were aligned after age 2. The data imply that binocular motion processing mechanisms in infantile esotropia patients are capable of some degree of recovery, and that this plasticity is restricted to a critical period of visual development.     

Lysosomal abnormalities in degenerating neurons link neuronal compromise to senile plaque development in Alzheimer disease

Antibodies to the lysosomal hydrolases, cathepsins B and D and β-hexosaminidase A, revealed alterations of the endosomal-lysosomal system in neurons of the Alzheimer disease brain, which preceded evident degenerative changes and became marked as atrophy, neurofibrillary pathology, or chromatolysis developed. At the earliest stages of cell atrophy, hydrolase-positive lysosomas accumulated at the basal pole and then massively throughout the perikarya and proximal dendrites of affected pyramidal neurons in Alzheimer prefrontal cortex and hippocampus, far exceeding the changes of normal aging. Secondary lysosomes as well as tertiary residual bodies (lysosomes/lipofuscin) increased implying stimulated, autophagocytosis and lysosomal system activation. Less affected brain regions, such as the thalamus, displayed similar though less extensive alterations. Certain thalamic neurons exhibited a distinctive lysosome-related abnormality characterized by the presence of cell surface blebs of varying size and number filled with intense hydrolase immunoreactivity. At more advanced stages of degeneration in still intact neurons, hydrolase-positive lipofuscin, particularly in the form of abnormal large aggregates, nearly filled the cytoplasm. Similar lipofuscin aggregates were oberved in abundance in the extracellular space following cell lysis and were usually associated with deposits of the β-amyloid protein. Degenerating neurons and their processes were the major source of these aggregates within senile plaques which contained high concentrations of acid hydrolases. We have shown in previous studies that these lysosomal hydrolases in plaques are enzymatically-active. The persistence of lysosomal structures in the brain parenchyma after neurons hyve degenerated is a striking and potentially diagnostic feature of Alzheimer disease which has not been observed, to our knowledge, in other degenerative diseases. The lysosomal response in degerating Alzheimer neurons represents a probable link between an early activation of the lysosomal system in at-risk, normal-appearing neurons and the end-stage contribution of lysosomes to senile plaque formation of emphasizes a slowly progressive disturbance of the lysosomal system throughout the development of Alzheimer disease.     

Multicolored Asian lady beetle hypersensitivity: a case series and allergist survey.

BACKGROUND: Multicolored Asian lady beetles (Harmonia axyridis) have been used as a biological control agent against crop-destroying aphids in the United States. Outside their natural habitat, H. axyridis seeks refuge in homes during fall and winter, leading to patient complaints and symptoms of rhinitis, wheezing, and urticaria on exposure to the beetles. OBJECTIVE: To gain a better understanding of the character and spectrum of allergic disease provoked by exposure to home-infesting lady beetles. METHODS: Eight patients with allergic symptoms suspected of being caused by H. axyridis and consistent with an IgE-mediated process were identified and interviewed. A whole-body extract from H. axyridis was prepared. Western blots using the patients' serum identified specific IgE antibodies in the extract. Through a novel technique, immunohistochemical analysis using beetle sections overlayed with patient serum was performed. A random survey of allergists from across the United States was also performed to evaluate experience with cases of lady beetle allergy. RESULTS: Western blots revealed IgE binding to 5 proteins with molecular weights of approximately 8.6, 21, 28, 31, and 75 kDa. Specific IgE bound to proteins localized in the beetle's mouth and leg areas. The allergist survey revealed positive responses in North Central, Mid-Atlantic and New England states. CONCLUSION: In 8 patients with allergic symptoms on exposure to high levels of lady beetles, specific IgE bound to proteins from H. axyridis. There was also an increased frequency of suspected cases of lady beetle allergy in endemic areas.