CHAPTER 50 ■ ODOR: UNUSUAL ALISON ST GERMAINE BRENT INTRODUCTION The human nose can discriminate approximately 4,000 odors! Occasionally, parents bring an infant or a child to the emergency department (ED) complaining of an unusual smell Adolescents are more likely to note a new or an unusual odor themselves and present to the ED with specific complaints Before the development of sophisticated laboratory tests, clinicians relied heavily on the sense of smell and often made clinically perceptive diagnoses by aroma alone Today, by incorporating the sense of smell into a clinical skill set, an astute provider can make a presumptive diagnosis of a metabolic disorder, intoxication, or infection, and institute lifesaving therapy prior to laboratory confirmation The incidence of an unusual odor is dependent on the underlying cause For example, in diabetic ketoacidosis (DKA), with an incidence of 80 to 150 per 1,000 person-years, the distinctive aroma of acetones is identified in approximately 30% of children at the time of initial diagnosis of diabetes mellitus By contrast, patients with inborn errors of metabolism (IEM) have an incidence of in 1,400 births with only a very small percentage being associated with abnormal odors (see Chapter 95 Metabolic Emergencies ) PATHOPHYSIOLOGY The olfactory area extends from the roof of the nasal cavity approximately 10 mm down the septum and superior turbinates bilaterally The exact mechanism of stimulation of the olfactory receptors is unknown Smell is more acute in the darkness and is believed to be linked to blood cortisol levels The unique odor emitted by a person is produced by a combination of body secretions and excretions, particularly those from the oropharynx, nasopharynx, and the respiratory tract, plus aromas from the skin and cutaneous lesions, urine, feces, and flatus The most significant components of odor in healthy humans are the apocrine glands These secretions are initially odorless, but bacterial breakdown that results in fatty acid production can cause an offensive odor Body odor is altered by hygiene, metabolism, toxins, infections, and systemic disease When a child is unable to detect odor, anosmia should be considered When a child complains of strange odors, especially if no one else can identify them,