Survey on Olfactory Testing by Pediatric Neurologists: Is the Olfactory a "True" Cranial Nerve?

Background: The olfactory nerve was conceptualized in the 4th century BC by Alcmaeon and described anatomically by Winslow in 1733. Cranial nerves (CNs) were named and numbered by Soemmerring in 1791. Notions still prevail that the olfactory (CN1) is not a "true" cranial nerve.

Methods: To confirm our impression that the olfactory nerve is infrequently tested by North American pediatric neurologists, a survey was distributed to members of national pediatric neurology societies in Mexico, Canada, and the United States. A total of 233 responses were received to 6 multiple-choice questions regarding practice patterns examining CN1 in neonates and children and in metabolic, endocrine, and genetic disorders and cerebral malformations. Two of the questions addressed familiarity with neonatal olfactory reflexes and asked whether the olfactory is a "true" cranial nerve.

Results: Only 16% to 24% of North American pediatric neurologists examine CN1 in neonates, even in conditions in which olfaction may be impaired. About 40% of respondents were aware of olfactory reflexes. A minority 15% did not consider CN1 as a "true" cranial nerve.

Conclusions: Olfactory evaluation in neonates is simple, rapid, and inexpensive. It tests parts of the brain not otherwise examined. It may assist diagnosis in cerebral malformations; metabolic, endocrine, and hypoxic encephalopathies; and some genetic diseases, including chromosomopathies. CN1 is neuroanatomically unique and fulfills criteria of a true sensory cranial nerve. We recommend that olfaction be routinely or selectively included during neurologic examination of neonates and children.