Definition of anosmia and paraosnia with disease
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Anosmia and Parosmia: Definitions and Associated Diseases
Classification of Olfactory Disturbances
Olfactory disturbances are divided into four groups (Adams and Victor's Principles of Neurology, 12th Ed.):
| Type | Description |
|---|---|
| Quantitative | Loss or reduction of smell (anosmia, hyposmia) or increased acuity (hyperosmia) |
| Qualitative | Distortion or illusion of smell (parosmia / dysosmia) |
| Hallucinations | Smelling odors with no stimulus (phantosmia), from temporal lobe/psychiatric disease |
| Higher-order loss | Olfactory agnosia - can detect but cannot recognize odors |
ANOSMIA
Definition
Anosmia is the complete loss of the sense of smell. It is the most frequent clinical abnormality of olfaction. If unilateral, it often goes unrecognized by the patient. Bilateral anosmia leads the patient to believe taste is also lost (ageusia), because flavor perception depends heavily on olfactory detection of volatile food particles through the nasopharynx.
- K.J. Lee's Essential Otolaryngology: "Anosmia - inability to detect all odors"
- Prevalence of functional anosmia in the general population: approximately 5%; hyposmia approximately 20%
Categories of Anosmia
| Category | Mechanism |
|---|---|
| Nasal | Odorants fail to reach olfactory receptors |
| Olfactory neuroepithelial | Destruction of receptors or their axon filaments |
| Central | Lesions along the olfactory pathway |
Diseases and Causes of Anosmia
Nasal Causes
- Heavy smoking (most common cause of hyposmia in practice)
- Chronic rhinitis (allergic, atrophic, cocaine-induced, infectious - herpes, influenza, COVID-19)
- Nasal polyposis
- Overuse of topical vasoconstrictors
- Chronic atrophic rhinitis; sinusitis (allergic, vasomotor, infective)
Olfactory Epithelium / Neuroepithelial Causes
- Head injury with tearing of olfactory filaments (anterior cranial fossa fractures)
- Cranial surgery
- Subarachnoid hemorrhage, meningitis
- Toxic: organic solvents, aminoglycosides, tetracyclines, corticosteroids, methotrexate, opiates, L-dopa
- Metabolic: thiamine deficiency, adrenal and thyroid deficiency, cirrhosis, renal failure
- Wegener granulomatosis
- Compressive/infiltrative lesions: craniopharyngioma, meningioma (olfactory groove), aneurysm, meningoencephalocele
Central Causes
- Neurodegenerative diseases: Parkinson disease, Alzheimer disease, Huntington disease, Lewy body dementia
- Early neuropathologic changes in many neurodegenerative diseases begin in olfactory structures (Braak staging), making anosmia a very early marker
- Temporal lobe epilepsy
- Malingering and hysteria
Congenital / Syndromic Causes (Localization in Clinical Neurology, 8th Ed.)
- Kallmann syndrome (congenital anosmia + hypogonadotropic hypogonadism) - most classic association
- Turner syndrome
- Down syndrome
- Familial dysautonomia
- CHARGE syndrome
- Cleft palate (in men)
Infectious Causes
- COVID-19 (SARS-CoV-2) - one of the hallmark symptoms; ~50% of patients affected
- Upper respiratory viral infections (influenza, human orthopneumovirus, coronaviruses)
- Herpes simplex meningoencephalitis
- HIV infection
Endocrine / Metabolic
- Adrenal insufficiency
- Diabetes mellitus
- Hypothyroidism
- Pseudohypoparathyroidism
Toxic Metals
- Zinc, cadmium, chromium, nickel, gold, manganese
Iatrogenic
- Ethmoidectomy, rhinoplasty, temporal lobectomy, orbitofrontal lobectomy, submucous resection, radiotherapy, postlaryngectomy
PAROSMIA (also called Dysosmia)
Definition
Parosmia (from Greek para = beside/distorted + osme = smell) is a qualitative olfactory disturbance in which odors are present but are incorrectly perceived - typically pleasant or neutral smells are distorted into unpleasant or foul ones.
- Adams and Victor's Principles of Neurology: "Distortions of odor perception where an odor is present"
- K.J. Lee's Essential Otolaryngology: "Odor stimulus is present, but incorrectly identified - often mistaking pleasant or neutral odors for unpleasant ones"
- Cummings Otolaryngology: Approximately 5-10% of patients with olfactory dysfunction spontaneously report parosmia; focused investigation shows an even higher incidence
Parosmia vs. Phantosmia
| Feature | Parosmia | Phantosmia |
|---|---|---|
| Stimulus present? | Yes | No |
| Perception | Distorted (real odor smells wrong) | Hallucinated (smells something not there) |
| Typical quality | Unpleasant/foul | Often unpleasant |
| Origin | Peripheral + central | Likely central (hyperactive neurons, deafferentation) |
Pathogenesis
The exact mechanism is unclear. Two main theories (Cummings Otolaryngology):
- Partial loss of olfactory receptor neurons (ORNs) - incomplete loss allows stimulus detection but interferes with encoding, altering the perceived quality
- Altered central nervous system processing of olfactory information
Parosmia is often seen as a sign of recovery within the olfactory system (a positive prognostic indicator compared to phantosmia, which may indicate poor prognosis).
Diseases and Causes of Parosmia
| Category | Specific Conditions |
|---|---|
| Post-infectious (most common) | COVID-19, influenza, upper respiratory viral infections (onset typically 1-3 months after infection - PIOD) |
| Head injury | Tearing/partial injury of olfactory bulbs |
| Sinonasal disease | Chronic sinusitis, nasal infections |
| Psychiatric | Depression, psychotic illness (cacosmia - every food smells foul) |
| Neurological | Parkinson disease, Alzheimer disease, multiple sclerosis, traumatic brain injury |
| Epilepsy | Temporal lobe seizures (uncinate fits) - olfactory auras |
| Nutritional deficiencies | Zinc deficiency, Vitamin A deficiency (also cause hypogeusia and dysgeusia) |
| Endocrine/Metabolic | Adrenal insufficiency, diabetes mellitus, hypothyroidism, pseudohypoparathyroidism, cystic fibrosis, sarcoidosis |
| Toxic | Environmental exposures |
| Idiopathic | No identifiable cause in some cases |
A specific subtype, cacosmia, is the perception of foul or rotten smells and is particularly associated with psychiatric disorders (depression, psychosis).
Treatment of Parosmia
- Olfactory training (most evidence-based approach)
- Vitamins and zinc (claims unverified; zinc may interfere with copper absorption)
- Neuroleptic or antiepileptic drugs (unpredictable results)
- Repeated anesthetization of nasal mucosa may reduce the disturbance
- Addressing the underlying cause
- Spontaneous resolution occurs in many cases (average duration ~3 months)
Key Clinical Associations Summary
| Disease | Anosmia | Parosmia |
|---|---|---|
| COVID-19 / viral URTI | Yes | Yes (delayed onset 1-3 months) |
| Parkinson disease | Yes (early marker) | Yes |
| Alzheimer disease | Yes (early marker) | Yes |
| Kallmann syndrome | Yes (defining feature) | - |
| Head trauma | Yes | Yes |
| Temporal lobe epilepsy | Yes | Yes (aura) |
| Hypothyroidism | Yes | Yes |
| Zinc deficiency | Yes (hyposmia) | Yes |
| Depression/Psychosis | - | Yes (cacosmia) |
Sources: Adams and Victor's Principles of Neurology, 12th Ed. | Cummings Otolaryngology Head and Neck Surgery | K.J. Lee's Essential Otolaryngology | Localization in Clinical Neurology, 8th Ed. | Harrison's Principles of Internal Medicine 22nd Ed.
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In which chapter has anosmia and paraosmia topic
Looking at the table of contents from your textbook "Clinical-Competency Textbook of Śālākya Tantra: Śiro-Karṇa-Nāsā-Mukha Roga", the topic of anosmia and parosmia falls under:
Chapter 46 – Dīptādi Nāsāroga (Page 235)
Term 2, Periodic Assessment - 6
Why Chapter 46?
- Dīptādi Nāsāroga covers nasal diseases classified under the Dīpta group and related conditions
- Anosmia (loss of smell) and parosmia (distorted smell) are Nāsā (nasal) Roga - diseases of the nose and olfactory system
- In Āyurvedic Śālākya Tantra, disorders of the Ghrāṇendriya (olfactory sense organ) including smell abnormalities are grouped under nasal diseases
Also relevant is Chapter 34 - Nāsā Śārīra, Ghrāṇendriya and Nidāna Pañcaka (Page 60, Term 1), which covers the anatomy and physiology of the olfactory organ (Ghrāṇendriya) - this chapter lays the foundational understanding before the disease chapters.
In summary:
| Chapter | Topic | Page | Relevance |
|---|---|---|---|
| 34 | Nāsā Śārīra, Ghrāṇendriya and Nidāna Pañcaka | 60 | Anatomy & physiology of smell (foundation) |
| 46 | Dīptādi Nāsāroga | 235 | Main chapter for anosmia & parosmia |
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