Initiation of smell function in patients with congenital hyposmia

The olfactory test established by Henkin: is it reliable and does it correlate to established psychophysical tests?

PURPOSE

This pilot study aimed to determine whether the Henkin olfactory test discriminates between the olfactory function of patients with olfactory loss and healthy individuals, and whether the Henkin test is correlated with a validated psychophysical olfactory test.

METHODS

Participants underwent olfactory testing using the modified Henkin test (including detection [DT] and recognition [RT] thresholds, magnitude estimation [ME], and hedonic ratings [H], for four different odors) and the extended "Sniffin' Sticks" test battery (odor detection, discrimination, identification).

RESULTS

Forty-four individuals (28 women, aged 19-81 years, mean: 39 years) were included. Twenty-three were healthy (mean age: 38 years) and 21 had olfactory dysfunction (OD) (mean age: 40 years). OD patients had worse mean DT, lower composite RT, and lower ME ratings. Mean and individual odor H ratings were not significantly different between the groups. Most individuals were classified as hyposmic when using the prescribed classification by Henkin, with only very few satisfying the stringent criteria of anosmia and normosmia. Modified Henkin subtests were all positively correlated with each other and with the "Sniffin' Sticks", except for Unpleasant Mean H which was only correlated with Pleasant Mean H; and Pleasant mean H which was not correlated with mean DT scores.

CONCLUSION

The Henkin test is able to separate between OD patients and controls. However, modifications to the conduct of this test may be required. Studies that used this test should be carefully interpreted.

LEVEL OF EVIDENCE: 3

International consensus statement on allergy and rhinology: Olfaction

BACKGROUND

The literature regarding clinical olfaction, olfactory loss, and olfactory dysfunction has expanded rapidly over the past two decades, with an exponential rise in the past year. There is substantial variability in the quality of this literature and a need to consolidate and critically review the evidence. It is with that aim that we have gathered experts from around the world to produce this International Consensus on Allergy and Rhinology: Olfaction (ICAR:O).

METHODS

Using previously described methodology, specific topics were developed relating to olfaction. Each topic was assigned a literature review, evidence-based review, or evidence-based review with recommendations format as dictated by available evidence and scope within the ICAR:O document. Following iterative reviews of each topic, the ICAR:O document was integrated and reviewed by all authors for final consensus.

RESULTS

The ICAR:O document reviews nearly 100 separate topics within the realm of olfaction, including diagnosis, epidemiology, disease burden, diagnosis, testing, etiology, treatment, and associated pathologies.

CONCLUSION

This critical review of the existing clinical olfaction literature provides much needed insight and clarity into the evaluation, diagnosis, and treatment of patients with olfactory dysfunction, while also clearly delineating gaps in our knowledge and evidence base that we should investigate further.

Nitric oxide signalling in the brain and its control of bodily functions

Nitric oxide (NO) is a versatile molecule that plays key roles in the development and survival of mammalian species by endowing brain neuronal networks with the ability to make continual adjustments to function in response to moment-to-moment changes in physiological input. Here, we summarize the progress in the field and argue that NO-synthetizing neurons and NO signalling in the brain provide a core hub for integrating sensory- and homeostatic-related cues, control key bodily functions, and provide a potential target for new therapeutic opportunities against several neuroendocrine and behavioural abnormalities.

Olfactory Development, Part 1: Function, From Fetal Perception to Adult Wine-Tasting

Discrimination of odorous molecules in amniotic fluid occur after 30 weeks' gestation; fetuses exhibit differential responses to maternal diet. Olfactory reflexes enable reliable neonatal testing. Olfactory bulbs can be demonstrated reliably by MRI after 30 weeks' gestation, and their hypoplasia or aplasia also documented by late prenatal and postnatal MRI. Olfactory axons project from nasal epithelium to telencephalon before olfactory bulbs form. Fetal olfactory maturation remains incomplete at term for neuronal differentiation, synaptogenesis, myelination, and persistence of the transitory fetal ventricular recess. Immaturity does not signify nonfunction. Olfaction is the only sensory system without thalamic projection because of its own intrinsic thalamic equivalent. Diverse malformations of the olfactory bulb can be diagnosed by clinical examination, imaging, and neuropathology. Some epileptic auras might be primarily generated in the olfactory bulb. Cranial nerve 1 should be tested in all neonates and especially in patients with brain malformations, endocrinopathies, chromosomopathies, and genetic/metabolic diseases.

On the mechanism of smell loss in patients with Type II congenital hyposmia

BACKGROUND

Smell function has been initiated with theophylline treatment in 63% of patients with Type II congenital smell loss. Based upon a systematic evaluation of the protein components of nasal mucus we have demonstrated that interactions among four chemical moieties in nasal mucus may play significant roles in this initiation. Prior to treatment three of these moieties, cAMP, cGMP and sonic hedgehog (Shh), were significantly decreased in concentration whereas one of these moieties, TNFalpha, was increased in concentration. The mechanism(s) responsible for initiation of smell function in these patients, not immediately apparent, may depend upon understanding interactions among these moieties.

METHODS

Measurements of cAMP, cGMP, Shh and TNFalpha in nasal mucus by specific spectrophotometric immunoassays before and after treatment with theophylline.

RESULTS

Before theophylline treatment cAMP, cGMP and Shh in nasal mucus, which act as growth factors to support olfactory receptor function, were significantly decreased below normal levels whereas TNFalpha which acts as a "death factor" to inhibit olfactory receptor function was significantly increased above normal. After theophylline treatment cAMP, cGMP and Shh increased significantly whereas TNFalpha decreased significantly.

CONCLUSIONS

These results indicate that there are specific biochemical changes associated with smell loss in patients with Type II congenital smell loss and that correction of these biochemical changes are associated with initiation of smell function in these patients. Understanding these relationships play an important role in understanding receptor action in smell function.