Developing reference data for nerve conduction studies: An application of quantile regression

Introduction: The interpretation of nerve conduction studies, as with any diagnostic test, requires an ability to differentiate normal from abnormal. To this end there have been many efforts to establish reference or normative data, but they have been hampered by a variety of methodological shortcomings. The goal of this article is to introduce a statistical method known as quantile regression, which we contend is better suited than existing methods to generate reference data, especially when there is a need to adjust for covariates. Methods: Statistical methods previously used for generation of reference data are reviewed. Quantile regression is presented and used to estimate the lower percentiles for response amplitudes of the radial sensory and tibial motor nerves. Results: Using data from 190 subjects, it is possible to estimate as low as the 2nd percentile for the radial nerve. Using data from 99 subjects it is possible to estimate as low as the 4th percentile for the tibial nerve. Percentile estimation for both nerves required adjustment for age, but no other covariates. Discussion: Quantile regression is well suited to the estimation of extreme percentiles, the very percentiles that are most relevant to reference data. It is also less dependent on data distribution and permits covariate adjustment, even for continuous variables such as age, which are clinically important determinants of reference data for nerve conduction studies. We recommend the use of quantile regression for future studies of reference data. Muscle Nerve 40: 763–771, 2009     

Huntington's disease: a randomized,controlled trial using the NMDA-antagonist amantadine

OBJECTIVE: To examine the acute effects of the NMDA receptor antagonist amantadine on motor and cognitive function in Huntington's disease (HD). BACKGROUND: Chorea in HD and in the levodopa-induced dyskinesias of PD may be clinically indistinguishable. In PD, hyperphosphorylation of NMDA receptors expressed on striatal medium spiny neurons contributes to peak-dose dyskinesias, and drugs that block these receptors can diminish chorea severity. Because these spiny neurons are the primary target of the neurodegenerative process in HD, sensitization of NMDA receptors on residual striatal neurons might also participate in the generation of motor dysfunction in HD. METHODS: To evaluate this possibility, 24 patients with HD entered a double-blind placebo-controlled crossover study of amantadine with two 2-week arms. RESULTS: Chorea scores were lower with amantadine (usually 400 mg/d) than placebo, with a median reduction in extremity chorea at rest of 36% (p = 0.04) for all 22 evaluable patients and of 56% in the 10 individuals with the highest plasma drug levels. Improvement correlated with plasma amantadine concentrations (p = 0.01) but not CAG repeat length. Parkinsonian rating scores did not worsen and there was no consistent change in cognitive measures. Adverse event profile was benign. CONCLUSIONS: Results suggest that NMDA receptor supersensitivity may contribute to the clinical expression of choreiform dyskinesias in HD and that selective antagonists at that site can safely confer palliative benefit.     

Radiation-induced second cancers: the impact of 3D-CRT and IMRT

Information concerning radiation-induced malignancies comes from the A-bomb survivors and from medically exposed individuals, including second cancers in radiation therapy patients. The A-bomb survivors show an excess incidence of carcinomas in tissues such as the gastrointestinal tract, breast, thyroid, and bladder, which is linear with dose up to about 2.5 Sv. There is great uncertainty concerning the dose-response relationship for radiation-induced carcinogenesis at higher doses. Some animal and human data suggest a decrease at higher doses, usually attributed to cell killing; other data suggest a plateau in dose. Radiotherapy patients also show an excess incidence of carcinomas, often in sites remote from the treatment fields; in addition there is an excess incidence of sarcomas in the heavily irradiated in-field tissues. The transition from conventional radiotherapy to three-dimensional conformal radiation therapy (3D-CRT) involves a reduction in the volume of normal tissues receiving a high dose, with an increase in dose to the target volume that includes the tumor and a limited amount of normal tissue. One might expect a decrease in the number of sarcomas induced and also (less certain) a small decrease in the number of carcinomas. All around, a good thing. By contrast, the move from 3D-CRT to intensity-modulated radiation therapy (IMRT) involves more fields, and the dose-volume histograms show that, as a consequence, a larger volume of normal tissue is exposed to lower doses. In addition, the number of monitor units is increased by a factor of 2 to 3, increasing the total body exposure, due to leakage radiation. Both factors will tend to increase the risk of second cancers. Altogether, IMRT is likely to almost double the incidence of second malignancies compared with conventional radiotherapy from about 1% to 1.75% for patients surviving 10 years. The numbers may be larger for longer survival (or for younger patients), but the ratio should remain the same.     

Frequency and Distribution of DNA fragmentation in Hashimoto’s thyroiditis and development of papillary thyroid carcinoma

Downregulation of apoptosis and high expression of bcl-2 play an important role in the development of follicular lymphoma. However, little is known about apoptosis in thyroid disease, particularly with respect to the development of papillary carcinoma from Hashimoto’s thyroiditis. To study the early stages of cell death in various types of thyroid disease, surgical specimens from 31 patients including Hashimoto’s thyroiditis (HT,n=7), papillary carcinoma (PC,n=12), Hashimoto’s thyroiditis with papillary carcinoma (HTPC,n=5), and Graves’ disease (GD,n=7) were examined by anin situ nucleotidyl transferase assay (ISNTA), which detects DNA fragmentation. Control normal thyroid tissue (NT,n=7) was obtained from surgically resected papillary thyroid carcinomas sampled away from the primary tumor. An immunohistochemical (IHC) method was used to detect bcl-2 expression. Positive ISNTA nuclei in thyroid follicular cells or tumor cells per section were counted in all parenchymal areas, excluding areas of lymphocyte aggregates. The intensity of bcl-2 staining was graded on a scale of 1+ to 3+. The number of ISNTA-positive thyroid follicular cells was a significantly higher in HT compared to GD. In addition, there was significantly lower number of ISNTA positive non-neoplastic thyroid follicular cells in HTPC compared to HT alone. Strong expression of bcl-2 was found in all cases of GD and NT, but much less bcl-2 staining was seen in HT. There was moderate expression of bcl-2 in HTPC and PC. These findings suggest that (1) DNA fragmentation of the thyroid follicular cells plays an important role in the thyroid injury in HT but not in GD, (2) expression of bcl-2 may overcome the apoptosis in GD but not in HT, and (3) downregulation of DNA fragmentation of the follicular cells in Hashimoto’s thyroiditis associated with papillary carcinoma may suggest an important mechanism for tumor pathogenesis.     

A pseudo-cryptococcal artefact derived from leucocytes in wet India ink mounts of centrifuged cerebrospinal fluid.

Wet India ink mounts of cerebrospinal fluid (CSF) are useful in the laboratory diagnosis of cryptococcal meningitis. Pseudo-cryptococcal artefacts in such mounts have been attributed to leucocytes in CSF but their mode of formation has not been explained. This report describes the reproduction of such an artefact in cryptococcus free CSF-leucocyte mixtures that had been subjected to high speed centrifugation. The viscosity of DNA that could provide a morphological pseudo-capsule, and the yellow-green fluorescence of the pseudo-capsular material on staining with acridine-orange, suggest that lymphocytic nuclear DNA, which possibly leaked out after damage to the lymphocyte membrane by centrifugation, was responsible for this artefact.     

Reduction of cortical TrkA but not p75(NTR) protein in early-stage Alzheimer's disease

Degeneration of cholinergic nucleus basalis (NB) cortical projection neurons is associated with cognitive decline in late-stage Alzheimer's disease (AD). NB neuron survival is dependent on coexpression of the nerve growth factor (NGF) receptors p75(NTR) and TrkA, which bind NGF in cortical projection sites. We have shown previously a significant reduction of NB perikarya expressing p75(NTR) and TrkA protein during the early stages of AD. Whether there is a concomitant reduction in cortical levels of these receptors during the progression of AD is unknown. p75(NTR) and TrkA protein was evaluated by quantitative immunoblotting in five cortical regions (anterior cingulate, superior frontal, superior temporal, inferior parietal, and visual cortex) of individuals clinically diagnosed with no cognitive impairment (NCI), mild cognitive impairment (MCI), mild/moderate AD, or severe AD. Cortical p75(NTR) levels were stable across the diagnostic groups. In contrast, TrkA levels were reduced approximately 50% in mild/moderate and severe AD compared with NCI and MCI in all regions except visual cortex. Mini-Mental Status Examination scores correlated with TrkA levels in anterior cingulate, superior frontal, and superior temporal cortex. The selective reduction of cortical TrkA levels relative to p75(NTR) may have important consequences for cholinergic NB function during the transition from MCI to AD.     

Preservation of brain nerve growth factor in mild cognitive impairment and Alzheimer disease

BACKGROUND: The status of nerve growth factor (NGF) levels during the prodromal phase of Alzheimer disease (AD), characterized by mild cognitive impairment (MCI), remains unknown. OBJECTIVE: To investigate whether cortical and/or hippocampal NGF levels are altered in subjects with MCI or different levels of AD severity. DESIGN AND MAIN OUTCOME MEASURES: An NGF enzyme-linked immunosorbent assay determined protein levels in the hippocampus and 5 cortical areas in people clinically diagnosed as having no cognitive impairment, MCI, mild AD, or severe AD. SETTING AND PATIENTS: Subjects were from the Rush Religious Orders Study and the University of Pittsburgh Alzheimer's Disease Research Center (Pittsburgh, Pa). RESULTS: We found no changes in cortical or hippocampal NGF levels across groups; in MCI, levels did not correlate with an increase in choline acetyltransferase activity in these regions. CONCLUSION: Brain NGF levels appear sufficient to support the cholinergic plasticity changes seen in MCI and remain stable throughout the disease course.     

Ethnic differences in breast cancer risk: a possible role for pregnancy levels of alpha-fetoprotein?

BACKGROUND: Breast cancer incidence rates are up to five times higher in white women in the United States compared with Asian women in China and Japan. A search for factors that modify estrogen's biological effect differentially between ethnic groups may add to the understanding of international variations in breast cancer risk. Recent evidence indicates that alpha-fetoprotein, a glycoprotein produced by the fetal liver, has important antiestrogenic properties. During pregnancy, alpha-fetoprotein reaches peak concentrations in maternal serum during the third trimester. METHODS: We compared pregnancy levels of alpha-fetoprotein in a population with high risk of breast cancer (Boston, MA) and low risk (Shanghai, China). Blood samples were collected around the 16th week and around the 27th week of gestation among women enrolled from March 1994 to October 1995. The number of specimens available for alpha-fetoprotein analysis was 1,033. RESULTS: Alpha-fetoprotein levels, adjusted for gestational length, were substantially higher in Shanghai compared with Boston women at both time points. When adjustments were made for prepregnancy weight, parity, offspring's sex and maternal age, alpha-fetoprotein levels remained 13% higher in Shanghai at 16 weeks of pregnancy but not at 27 weeks. CONCLUSIONS: These findings may explain, at least in part, the difference in breast cancer risk between Chinese and American women. On the population level, alpha-fetoprotein may influence risk by modifying the effect of biologically active estrogens both in the mother and in female offspring.