Adaptive Tree Proposals for Bayesian Phylogenetic Inference

Bayesian inference of phylogeny with MCMC plays a key role in the study of evolution. Yet, this method still suffers from a practical challenge identified more than two decades ago: designing tree topology proposals that efficiently sample tree spaces. In this article, I introduce the concept of adaptive tree proposals for unrooted topologies, that is tree proposals adapting to the posterior distribution as it is estimated. I use this concept to elaborate two adaptive variants of existing proposals and an adaptive proposal based on a novel design philosophy in which the structure of the proposal is informed by the posterior distribution of trees. I investigate the performance of these proposals by first presenting a metric that captures the performance of each proposal within a mixture of proposals. Using this metric, I compare the performance of the adaptive proposals to the performance of standard and parsimony-guided proposals on 11 empirical datasets. Using adaptive proposals led to consistent performance gains and resulted in up to 18-fold increases in mixing efficiency and 6-fold increases in convergence rate without increasing the computational cost of these analyses.

The effect of buttonhole cannulation vs. rope-ladder technique on hemodialysis access patency

The rope-ladder (RL) technique is the most common technique used for cannulation of arteriovenous fistulae (AVF). Buttonhole cannulation (BHC), or constant-site technique, is recommended by the National Kidney Foundation's Kidney Disease Outcome Quality Initiative (NKF/KDOQI) vascular access guidelines. We compared outcomes of primary patency, episodes of bacteremia, access blood flow (Qa), and quality of life (QoL) scores between RL and BHC patients. Using a prospectively collected, vascular access database, a total of 45 prevalent dialysis patients using BHC were compared with 38 patients using the RL technique over a median of 12 months (inter-quartile range: 4-27 months). The two groups did not differ significantly in demographics except that diabetes was more common in those using BHC as compared to rope-ladder (69% vs. 34%; p = 0.002). Risk factors associated with lack of primary patency were age (hazards ratio [HR] = 1.02 per decade; 95% CI: 1.00-1.03; p = 0.04) and female gender (HR = 1.92; 95% CI: 1.08-3.40; p = 0.03). Use of the buttonhole technique was not associated with improved primary patency (HR = 1.22, 95% CI: 0.65-2.28; p = 0.53). Episodes of bacteremia and mean scores from KDQOL-36 did not differ significantly between the groups. This study demonstrates for the first time that BHC use is not associated with improved access patency.

[Subacute meningoradiculomyeloencephalitis due to cryptococcosis infection]

INTRODUCTION

If meningoencephalitis with or without mass lesion (granuloma or abscess) is the most common pattern of CNS cryptococcal infection, intramedullary involvement is very uncommon.

EXEGESIS

The authors report an 70-year-old male with Hodgkin's disease treated by chemotherapy then corticosteroids because of pulmonary fibrosis who was presenting for eight days ago, an ataxia, pyramidal syndrome, and bradypsychy. Spinal MRI revealed a gadolinium T1 weighted homogeneous enhancing T4 level intramedullary lesion. CSF had showed 190 GB/mm3 of lymphomonocytes, increased protein level (2.28 g/l), decreased glucose level (1.5 mmol/l) and positivity for crytococcal antigen. Treatment by amphotericine B and flucytosine then fluconazole for six months was instituted and symptoms gradually improved.

CONCLUSION

A cryptococcus infection must be searched by antigen in CSF in case of myelopathy isolated or associated with meningoradiculoencephalomyelopathy, specially in patients with a cellular immunodeficience. Antimycotic agents must be firstly used, surgery would be restricted to decompression if aggravation of disease and compressive effect on the adjacent structures radiologically (MRI) became evident. Prolonged treatment is necessary in case of immunodeficience.

[Indications for the use of an epidural blood patch in the treatment of spontaneous intracranial hypotension]

We report a patient with spontaneous intracranial hypotension treated with an epidural blood patch (EBP) and discuss the indication of this procedure in the treatment of this syndrome. Once diagnosis has been established (symptoms, CSF pressure, MRI), we propose to wait no more than a week, when simple treatment options have failed, before proceeding to an EBP. We inject a minimum of 20 ml, until the appearance of pain while injecting, of autologous blood in the L3-L4 epidural space. If this technique is unsuccessful, T6 would appear to be the best level to perform an EBP because it is by far the most common location of dural leakage (cervico-dorsal junction) and because this choice is also in accordance with the fact the blood may spread over 10 vertebral segments on each side of the injection level. Spinal MRI should at best be done before the procedure but is absolutely required when the patient fails to respond to the EBP conducted in the conditions we propose.

[Acute severe leukoencephalitis with posterior lesions due to Borrelia burgdorferi infection]

INTRODUCTION

Central nervous system manifestations represent 0.54 to 8% of neurological complication in Lyme disease.

OBSERVATION

A 78-year-old woman presented a severe meningo-encephalitis with visual disorders (agnosia, alexia) progressing towards coma. Cranial magnetic resonance imaging revealed large areas of hypersignal T2 in the white matter of the lower, parieto-occipital lobes and left temporal lobe. The cerebrospinal fluid (CSF) contained 16 then 293 white corpuscles/mm3 of lympho-monocytes, increased protein level from 2.67 to 5.83 g/l and an increase in IgG index with oligoclonal distribution of IgG. Serological Elisa analysis for Lyme disease was slightly positive in blood (confirmed by western blot) but clearly in the CSF (IgG and IgM). Treatment with ceftriaxone followed by methylprednisolone provided clinical improvement 3 months later.

DISCUSSION

Acute meningo-encephalitis is often benign, protein-like and of good prognosis: the gnosic visual disorders with posterior leukoencephalopathy are unusual. A blood level of specific antibodies slightly positive on Elisa at the early stage of the infection warrants confirmation by Western blot in the blood and by Elisa in the CSF. Additional corticosteroid therapy may be required in the severe forms that evoke acute disseminated encephalomyelitis.

[Aneurysm of the superior mesenteric vein: imaging findings]

The authors report two uncommon cases of incidental superior mesenteric vein aneurysm in two asymptomatic women. Patients underwent ultrasonography, CT and MR angiography. The etiology, clinical features and treatment are discussed along with a review of to the literature.

[Magnetic resonance imaging of tibial periostitis]

Tibial periostitis frequently occurs in athletes. We present our experience with MRI in a series of 7 patients (11 legs) with this condition. The clinical presentation and scintigraphic scanning suggested the diagnosis. MRI exploration of 11 legs demonstrated a high band-like juxta-osseous signal enhancement of SE and IR T2 weighted sequences in 6 cases, a signal enhancement after i.v. contrast administration in 4. Tibial periostitis is a clinical diagnosis and MRI and scintigraphic findings can be used to assure the differential diagnosis in difficult cases with stress fracture. MRI can visualize juxta-osseous edematous and inflammatory reactions and an increased signal would appear to be characteristic when the band-like image is fixed to the periosteum.

[Diagnosis of a post-thrombophlebitic dural fistula using MR angiography]

We report a case in which MRA made it possible to diagnose a dural arteriovenous fistula and thrombophlebitis in a 23-year old woman. 2D TOF MRA is the usual technique in the diagnosis of thrombophlebitis. Our experience shows the limits of 2D TOF since the increased signal intensity in the sinus could simulate a normal flow, and we describe the advantages of MR subtraction angiography. In our study, 3D TOF MRA showed the dural arteriovenous fistula, its location near the right transverse sinus and some of the feeding vessels: tentorial branch of the internal carotid artery and meningeal branch of the right occipital artery. 3D TOF MRA provides the diagnosis of dural arteriovenous fistula, but it cannot replace the plain angiography performed before endovascular or surgical treatment.

[Unilateral adrenal hematoma in adults. Contribution of MRI in follow-up]

We describe a case of unilateral and spontaneous adrenal hematoma. Initial and follow up MRI examinations showed serial modifications typical of hematoma and allowed to exclude a preexisting non hyperfunctioning tumor. MRI findings modified the therapeutic attitude, a voiding surgery.