Quantitative vibration perception thresholds in patients under prolonged antiepileptic treatment

Effects of drugs on olfaction and taste

The fact that so many varied medications reportedly affect taste and smell is a testament to the complexity of the gustatory and olfactory systems. The reception, transduction, propagation, and perception of a chemical tastant or odorant requires the effective operation of numerous mechanisms--all of which may be susceptible in one way or another to a prescribed medication. Just as a diuretic may block the apical ion channels on a taste bud, or an antifungal can inhibit cytochrome p450-dependent enzymes at the level of the receptors, a chemotherapeutic agent can destroy mitosis in a replicating receptor cell and a steroid can lead to candidal overgrowth on the tongue surface. Medications not only have a perceivable taste themselves at times, but they can alter the mechanisms responsible for the ultimate perception of tastes and smells--either by direct or secondary means. It should be emphasized, as noted earlier in this article, that while many medications are to blame for the impairment or distortion of the gustatory or olfactory systems, it is not uncommon that the underlying medical problem for which they are prescribed is actually the culprit. Examples include epilepsy, migraines, hypothyroidism, schizophrenia, infections, and cancer. In fact, simple partial seizures emanating from regions of the brain such as the amygdala, hippocampus, parietal operculum, and rolandic operculum can lead to the chemosensory sensations that are most commonly considered unpleasant, such as "rotten apples," "cigarette," "peculiar," or "vomitus". While removing or changing an offending medication can reverse the effects on smell or taste perception, it is important to remember that lasting impairment may occur. This is vital for a physician to recognize prior to prescribing a medication. It is also necessary to report this to patients who may be devastated by chemosensory alterations after starting a new medication (eg, pastry chef, perfumist, wine specialist, plumber). Among the "risks" in a risks/benefits discussion with a patient regarding the use of a new medication, alterations in olfaction and taste appear to play an increasingly recognized role.

Differential Effects of Neuropathic Analgesics on Wind-up-like Pain and Somatosensory Function in Healthy Volunteers

OBJECTIVES

To investigate the effects of gabapentin, carbamazepine, and amitriptyline on temporal summation, simple nociceptive pain, and innocuous touch sensation in healthy volunteers.

METHODS

A placebo controlled four-way crossover double-blind randomized protocol was followed. Seventeen healthy subjects, male and female, aged 18 to 24, took part. Punctate pain, temporal summation pain to repeat punctate stimulation, and vibration detection threshold were assessed in triplicate. Study drugs were given as bedtime and early morning doses with assessments carried out midmorning.

RESULTS

Gabapentin and carbamazepine significantly reduced the intensity of temporal summation pain (P < 0.001 and P < 0.01 respectively), whereas amitriptyline significantly increased temporal summation pain (P < 0.001). None of the drugs affected pain produced by a single punctate stimulus (P > 0.05). Carbamazepine increased vibration detection thresholds (P < 0.05), but neither gabapentin nor amitriptyline had any detectable effect on vibration.

DISCUSSION

We have shown that gabapentin, carbamazepine, and amitriptyline, three pharmacologically different drugs, have distinct and quantifiable effects on somatosensory pathways in healthy volunteers. These findings provide a link between pharmacology of the study drugs and clinical effectiveness. The effects of gabapentin and carbamazepine on temporal summation pain show that these drugs can block centrally amplified wind-up pain in the absence of a neuropathic disorder.

Normative values of vibratory perception in 530 children, juveniles and adults aged 3-79 years

Impaired vibratory perception is an early and frequent finding in various neuropathies. Quantitative vibratory threshold assessment refines the diagnosis of neuropathies but is based on psychophysical techniques requiring patient cooperation. Large, age and sex matched normative data bases are needed to better identify abnormal vibratory perception. In this study vibratory perception was tested at the second metacarpal bone and above the first metatarsal bone of 530 children, juveniles and adults aged 3.3-79.2 years. Thresholds assessed with a 128 Hz graded Rydel-Seiffer tuning fork, TF, were compared to three Vibrameter values, the vibration perception thresholds, VPT, determined with increasing vibration stimuli, the vibration disappearance threshold, VDT, determined with decreasing supraliminal stimuli, and the vibration threshold VT which equals the mean of VPT and VDT. The influence of gender, age, body height, weight and skin temperature at the tested site on thresholds was studied. Retest reliability was tested in 73 children aged 3.3-6.9 years and in 20 volunteers aged 5.2-66.1 years who were also tested for the influence of pretest skin warming on thresholds and for differences between results of the left and right body side. TF, VPT, VDT, VT were closely correlated with each other (Spearman: -0.67<Rs<-0.47; P<0.01). The skin temperature, body side, weight and height did not influence thresholds. In adults, thresholds increased with age and were higher in men above the age of 50 than in women of the same age. Thresholds at the feet were higher than at the hands (Wilcoxon: P<0.001). Retest reliability was high and did not depend on the retest interval. The study provides important normative data for the widespread use of quantitative vibration testing.

Vibration disappearance threshold may be raised by measuring it

The influence of duration and intensity of the initial level of vibration on vibration perception threshold was studied in 15 healthy young subjects (aged 27.9 +/- 7.6 years) with a Vibrameter (Somedic AB Sweden). The threshold for increasing vibration corresponded well to the normal values published by the manufacturer. The thresholds for decreasing vibration were measured with three different starting conditions: starting from a low level of vibration, a high level, and from a low level sustained for one minute. Higher intensity and longer duration of the initial vibration raised the disappearance threshold significantly. Vibration disappearance thresholds can be influenced by measuring them. As a result, the investigation of the vibration sense calls for strict control over intensity and duration of the stimuli.

Vibratory perception threshold in patients with mild multiple sclerosis

The vibratory perception threshold (VPT) was measured bilaterally on both the upper and lower extremity in 69 patients with mild multiple sclerosis. In the case of the lower extremities the VPT measurements were closely correlated with qualitative vibratory perception measurements performed with a tuning fork; in the upper extremities the association was weak. The VPT was abnormal at least in one extremity in 38% of the patients. Quantitative VPT measurement seem to be a suitable technique for the detection of sensory symptoms of central origin.