Vestibulo-ocular reflex dynamics with head-impulses discriminates spinocerebellar ataxias types 1, 2 and 3 and Friedreich ataxia

OBJECTIVE

Although the diagnosis of inherited ataxias is ultimately genetic, this usually means an extensive and expensive process. This justifies the search for distinct clinical signs that may potentially help orient molecular diagnosis.

METHODS

We explored the vestibulo-ocular reflex (VOR) with the video Head Impulse Test in patients diagnosed with spinocerebellar ataxia (SCA) type 3 (n = 15), type 1 (n = 4) and type 2 (n = 4), Friedreich's ataxia (FA) (n = 9) and healthy controls (n = 40). We estimated the latency, regression (VORr) and instantaneous VOR gain at 40, 60 and 80 ms (VOR40, VOR60 and VOR80), and determined the latency, peak-velocity and occurrence rate of catch-up saccades triggered with head-impulses.

RESULTS

VOR latency was higher in FA (p < 0.001) and SCA3 (p = 0.02) as compared to controls, discriminating FA from other ataxic patients with an overall diagnostic accuracy of 88%. VORr, VOR40 and VOR60 were significantly lower in FA and SCA3 (p < 0.01). VOR80 was only significantly lower than controls in SCA3 (p < 0.01), discriminating these from other ataxic patients with an overall diagnostic accuracy of 78%. Covert saccades were only triggered in SCA3 but with low occurrence rate and peak velocity (11.1 ± 28.5% and 77.50 ± 15.30°/s) whereas overt saccades were present in all groups. VORr gain showed a negative correlation with disease severity evaluated with SARA (Spearman r = -0.46, p = 0.01).

CONCLUSIONS

vHIT provides phenotypic information that differentiates these autosomal ataxias and can serve as a strategy to orient genetic diagnosis. A correlation between VOR and SARA raises the possibility of using VOR gain as a neurophysiologic biomarker for disease severity.

Relationship of bispectral index values, haemodynamic changes and recovery times during sevoflurane or propofol anaesthesia in rabbits

The aim of this study was to determine and compare the degree of hypnosis achieved during propofol or sevoflurane anaesthesia in rabbits using bispectral index (BIS), and to evaluate its usefulness as a predictor of both haemodynamic changes during anaesthesia and recovery times. Twenty adult male New Zealand White rabbits, average weight 4.4 ± 0.4 kg, were used for this study. Animals were randomly allocated to one of two groups with 10 rabbits/group. An electroencephalographic recording was obtained from each conscious rabbit prior to drug administration. All animals received buprenorphine as a preanaesthetic medication (0.05 mg/kg, intravenous [i.v.]). Anaesthesia was induced with propofol (8 mg/kg, i.v.) in all animals; 10 rabbits were maintained with sevoflurane via inhalation (1 minimum alveolar concentration – end-tidal sevoflurane concentration of 3.7% – at a fresh gas flow rate of 3 L/min; group I), and 10 were maintained with i.v. propofol (0.6 mg/kg/min; group II). The rabbits were orotracheally intubated and spontaneous ventilation was maintained throughout the study (100% oxygen). After abdominal surgery through a ventral midline laparotomy, rabbits were allowed to recover from anaesthesia. Cardiovascular variables and BIS values were recorded at intervals throughout the procedure, as was the duration of recovery from anaesthesia.

In both groups, mean BIS values were significantly decreased immediately after induction, compared with baseline values obtained during consciousness. Anaesthetic depth (evaluated by clinical observation) was similar in both groups; however, group II rabbits had significantly higher ( P<0.001) BIS values from 30 s before incision until anaesthesia was discontinued. There was no significant difference in BIS recorded 1 and 5 min after incision as compared with values obtained 30 s before incision in either group.

During sevoflurane or propofol administration, correlations were found between BIS values and mean arterial blood pressure (MABP), and between BIS values and heart rate (HR).

Mean BIS values at discontinuation of administration of the anaesthetic agent were greater in group II (69.1 ± 6.0) than in group I (49.3 ± 2.2). However, recovery from anaesthesia was significantly longer in group II (38.4 ± 7.2 min) than in group I (11.5 ± 2.5 min).

In conclusion, BIS can be used to differentiate between conscious and unconscious states during anaesthesia in rabbits. BIS values derived from an electroencephalogram at the end of anaesthesia were not useful for predicting the speed of anaesthetic recovery in sevoflurane or propofol-anaesthetized rabbits undergoing abdominal surgery. Despite the correlation found between BIS and haemodynamic parameters, its usefulness as a predictor of clinically important changes in arterial blood pressure and HR in anaesthetized rabbits was limited.

Anticompensatory quick eye movements after head impulses: A peripheral vestibular sign in spontaneous nystagmus

BACKGROUND

Differentiating central from peripheral origins of spontaneous nystagmus (SN) is challenging. Looking for a simple sign of peripheral disease with the video Head Impulsive Test we noticed anti-compensatory eye movements (AQEM) in patients with peripheral etiologies of spontaneous nystagmus (SN). Here we assess the diagnostic accuracy of AQEM in differentiating peripheral from central vestibular disorders.

METHODS

We recorded the eye movements in response to horizontal head impulses in a group of 43 consecutive patients with acute vestibular syndrome (12 with central, 31 with peripheral disorders), 5 patients after acute vestibular neurectomy (positive controls) and 39 healthy subjects (negative controls). AQEM were defined as quick eye movements (peak velocity above 50°/s) in the direction of the head movement.

RESULTS

All patients with peripheral disorders and positive controls had AQEM (latency 231 ± 53 ms, amplitude 3.4 ± 1.4°, velocity 166 ± 55°/s) when their head was moved to the opposite side of the lesion. Central patients did not have AQEM. AQEM occurrence rate was higher in peripheral patients with contralesional (74 ± 4%, mean ± SD) in comparison to ipsilesional (1 ± 4%) impulses (p< 0.001). Overall diagnostic accuracy for differentiating central from peripheral patients was 96% (95% CI for AUC ROC curve: 0.90 to 1.0) for VOR gain and 100% (95% CI: 1.0 to 1.0) for AQEM occurrence rate.

CONCLUSIONS

These results suggest that AQEM are a sign of vestibular imbalance in a peripheral deficit. In addition to VOR gain they should be added to the evaluation of the head impulse test.

Bispectral index, spectral edge frequency 95% and median frequency recorded at varying desflurane concentrations in pigs

The objective of this study is to evaluate the usefulness of bispectral index (BIS), spectral edge frequency 95% (SEF) and median frequency (MED) in relation to a simple descriptive scale (SDS) as indicators of anaesthetic depth at different desflurane concentrations in swine. Sixteen pigs were randomly allocated to four groups. Electroencephalograms (EEG) were recorded during desflurane anaesthesia, and BIS, SEF and MED were calculated from the EEG. The agent was administered in pure oxygen at 1, 1.25, 1.5 and 1.7 MAC in randomized order. Anaesthetic depth was evaluated on a SDS. BIS decreased significantly (P<0.001) at the different anaesthetic dosages used. SEF decreased significantly (P<0.001) from basal to 1 MAC of desflurane. MED decreased significantly (P<0.001) from basal to 1 MAC and from 1 to 1.75 MAC. Good correlation was seen between SDS scores and BIS values and between SDS scores and MED values. BIS appeared to be useful to predict changes in anaesthetic depth at clinically used dosages of inhalant anaesthesia.

Nuclear DNA sequence specific to Leishmania (Viannia) subgenus: a molecular marker for species identification

As shown by RFLP analysis, there is a high variability in the beta-tubulin gene region of Leishmania sp. Such variability has been used in the identification of these parasites, establishing differences between subgenera of New World Leishmania. We have found a region of 500 bp (beta500) upstream of the coding region of the beta-tubulin gene that is present in all strains tested belonging to the L. (Viannia) subgenus. This region apparently is a repetitive sequence and we have shown that it is specific to the Leishmania (Viannia) subgenus. This sequence has no homology with the genomic DNA isolated from either the species belonging to the L. (Leishmania) subgenus or other Kinetoplastida, such as Trypanosoma cruzi, T. brucei, Leptomonas samueli, or Crithidia fasciciulata. The beta500 sequence showed sufficient variation to be used as a molecular marker in the identification of parasites. We established inter- and intrasubgenus differentiation and were able to discriminate at the species level in the Vianna subgenus. A PCR assay confirmed the specificity of the beta500 sequence.

The genomic fingerprinting of the coding region of the beta-tubulin gene in Leishmania identification

We have demonstrated the polymorphism of the beta-tubulin gene region in Leishmania and its value in the identification of the parasite. In this work we have shown that the coding region of the gene has sufficient variation to accurately discriminate these parasites at the subgenus level. Nevertheless, intrasubgenus diversity, for particular restriction enzymes, was found in New World Leishmania belonging to the Leishmania subgenus. For instance, differences were found between mexicana and amazonensis strains. A unique pattern at the species level was found in particular species of both subgenera, e.g. L. (L.) major strain P and L. (L.) tropica belonging to the Leishmania subgenus, and L. (V.) panamensis strain LS94 from the Viannia subgenus. Particular endonucleases are diagnostic in Leishmania species discrimination as in the case of PvuII for the mexicana and amazonensis. This variation evidenced in the beta-tubulin gene region of Leishmania also occurred in other Kinetoplastida e.g. Trypanosoma cruzi, Leptomonas spp. and Crithidia spp. Moreover, these organisms showed a different genomic fingerprinting for the beta-tubulin gene among them and also Leishmania. Thus, the polymorphism of the coding region of the beta-tubulin gene can be used as a molecular marker for the identification of Leishmania.