xRead - Olfactory Disorders (September 2023)

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PATEL et al.

TABLE VIII.14 Role of bloodwork in routine workup of OD

Clinical end point

Study

Year 2016

LOE Study design Study groups

Conclusions

SS test

“OD may be present in patients with vitamin B12 deficiency” Negative correlation of age with odor identification score

Derinet al

3

Retrospective, case-control

39 patients with low vitamin B12 levels 34 controls

LOE = level of evidence; OD = olfactory dysfunction; SS = Sniffin’ Sticks.

unsafe nutritional intake of zinc is relatively narrow, 1294 bearing in mind that anosmia has been associated with the use of zinc-containing nasal gels or sprays, leading to a warning by the US Food and Drug Administraion (FDA) in June 2009. These products have since been taken off the market. 1295 Both hypogonadotropic hypogonadism, ie, Kallmann syndrome, and Klinefelter syndrome are associated with anosmia. Kallmann syndrome occurs more often in males than in females, with an estimated prevalence of 1 in 30,000 males and 1 in 120,000 females, and is associated with microphallus, cryptorchidism/small testes, delayed puberty, and delayed bone maturation. In their study, Dis saneevate et al 1296 showed that 56% had a family his tory of either anosmia or infertility. Laboratory diagno sis is based on a constellation of low serum levels of testosterone, luteinizing hormone, and follicle-stimulating hormone. 1296–1299 This hormone profile rules out a pri mary testicular disorder. However, before diagnosing con genital hypogonadotropic hypogonadism, it is important to rule out a pituitary tumor (by imaging studies), juve nile hemochromatosis, or any systemic condition, affect ing gonadotropin secretion and pubertal development. 1297 With genetic testing becoming more readily available, this will also be an avenue of laboratory investigation per formed by specialist services. Various neurologic conditions can present with loss of sense of smell, such as PD and AD. 1300 Although no blood tests exist for PD at present, a promising blood test for AD has been recently developed. 1301 When dealing with other causes of OD, eg, toxins, such as heavy metals or lead, 320 Sjögren syndrome, 398 DM, 1302 Wilson disease, 1303 and liver cirrhosis, 1304 clinical suspicion needs to guide the physician on which test(s) to order or whether to refer the patient to a colleague with expertise in a specific underly ing etiology. Recently, there has been an abundance of lit erature assessing symptoms of anosmia and dys geusia caused by COVID-19, with testing being indicated for hyposmia/anosmia and suspected COVID-19 infection. It is clear and in accordance with guidance from world and national public health organizations that

peripheral olfactory system, while simultaneously obtain ing psychophysical responses in awake humans. 1286 However, similar to other measures of chemosensory activation at the nasal mucosa, 1287,1288 the evidence level of EOG-related studies in a clinical context is currently low. More investigation is necessary to determine whether use of EOG in routine clinical practice would give additional useful clinical data, as well as determine how an EOG could be more easily utilized in routine clinical practice. Aggregate grade of evidence : C (Level 3 studies: two; Level 4 studies: one). G Role of bloodwork/lab values The literature on laboratory studies for evaluation and diagnosis of OD is sparse. This is likely why many previous position papers, such as the 2017 Position Paper on Olfac tory Dysfunction, 246 do not cover this topic. In the absence of systematic reviews and high-level evidence, lower evi dence reports and reasoning from first principles help to relate certain blood tests and laboratory studies to condi tions that are associated with OD. Derin et al 1289 shed light on the role of vitamin B12 in OD. In a case-control study, they showed that in the vita min B12–deficient group, hyposmia and anosmia were evi dent in 56.4% and 5.1% of the patients, respectively, but no patients in the control group had OD, suggesting a pos sible role for vitamin B12 blood testing in patients with hyposmia/anosmia (Table VIII.14). Vitamin B1 (thiamine) deficiency has also been implicated in OD, 1290 but no for mal study has assessed the role of vitamin B1 blood testing for the evaluation and diagnosis of anosmia. The evidence base for zinc deficiency as a cause for smell and taste dys function is also sparse. 1291,1292 Moreover, zinc nutritional status is difficult to adequately measure using laboratory tests. 1293 Present recommendations do not consider the numerous dietary factors that influence the bioavailability of zinc and copper and the likelihood of toxicity from zinc supplements. The current assumed range between safe and