Hyposmia

Hyposmia refers to a diminished sense of smell, a condition where an individual has difficulty detecting or identifying odors. This differs from anosmia, a more severe condition where there is a complete loss of the sense of smell. Olfactory disorders can greatly impact an individual's quality of life, affecting their ability to enjoy food, detect hazardous odors, or experience olfactory-related memories.

Definition and Comparison

• Hyposmia: A decreased sensitivity to some or all odors, it represents a range of impairment but is not a total loss.
• Anosmia: A total inability to perceive odors. It can be temporary or permanent, depending on the cause.

Causes and Risk Factors

There are various underlying causes and risk factors associated with hyposmia:

• Allergies: Inflammatory reactions can cause swelling in the nasal passages, reducing airflow and the ability to detect odors.
• Nasal Polyps: Benign growths in the nasal or sinus passages can obstruct airflow.
• Viral Infections: Infections, especially those of the upper respiratory tract, can damage or destroy olfactory neurons.
• Head Trauma: Injuries to the head can damage the olfactory nerve or the brain areas involved in smell.
• Chronic Conditions: Diseases like Parkinson's, Alzheimer's, and dementia with Lewy bodies are known to impact the olfactory system.

Epidemiology

It is estimated that up to 4 million individuals in the United States experience olfactory disorders, encompassing both hyposmia and anosmia. The prevalence increases with age, likely due to cumulative exposure to risk factors and age-related neurodegenerative conditions.

Association with Neurological Disorders

• Parkinson's disease: Hyposmia might manifest as one of the very early signs of Parkinson's disease, preceding motor symptoms by several years.
• Alzheimer's disease & Dementia with Lewy bodies: A reduced sense of smell is a frequent early symptom in both these conditions, reflecting the early involvement of olfactory structures and pathways in these diseases.
• Kallmann syndrome: This genetic condition is characterized by a reduced or absent sense of smell since birth, in addition to other symptoms like delayed or absent puberty.

Clinical Importance

Recognizing and diagnosing hyposmia is crucial not just for the direct impact on quality of life but also for its potential as an early marker for various neurological disorders. Moreover, understanding its underlying causes can guide effective treatments, ranging from addressing allergic reactions to surgical removal of nasal polyps.

References

• Doty, R.L. (2003). Handbook of Olfaction and Gustation. Marcel Dekker Inc.
• Haehner, A., Hummel, T., & Reichmann, H. (2009). Olfactory dysfunction as a diagnostic marker for Parkinson's disease. Expert Review of Neurotherapeutics, 9(12), 1773-1779.
• Murphy, C. (2019). Olfactory and other sensory impairments in Alzheimer disease. Nature Reviews Neurology, 15(1), 11-24.
• Boehm, U., Bouloux, P.M., & Dattani, M.T. (2015). Expert consensus document: European Consensus Statement on congenital hypogonadotropic hypogonadism--pathogenesis, diagnosis and treatment. Nature Reviews Endocrinology, 11(9), 547-564.

See also

• Hyperosmia
• Dysosmia
• Anosmia