Olfactory Training


Continuing Education Activity

Olfactory training is a non-pharmacological and non-surgical treatment for patients with olfactory dysfunction. Patients on olfactory training expose themselves twice daily to 4 different odors over at least 24 weeks. The main indications include postinfectious, posttraumatic, and idiopathic olfactory dysfunction and olfactory dysfunction due to idiopathic Parkinson disease. This activity reviews olfactory training and highlights the role of the interprofessional team in instructing and following the patients who do olfactory training.

Objectives:

  • Describe the physiology of olfactory training.
  • Identify the main indications for olfactory training.
  • Explain the protocol for olfactory training.
  • Summarize how an interprofessional team approach can provide patient benefit when performing olfactory training.

Introduction

About 20 percent of people in the general population have an impairment of their sense of smell.[1][2][3] Impaired olfaction leads to diminished quality of life. It can be dangerous as the individual affected may miss environmental hazards such as the smell of natural gas or smoke from the fire.[4] Also, diminished olfaction may a warning sign for common neurodegenerative disorders, such as Alzheimer's dementia and idiopathic Parkinson disease.[5][6] The most common causes of olfactory decline are olfactory decline secondary to sinonasal disease, post-infectious olfactory dysfunction, and post-traumatic olfactory dysfunction.[7][8] 

If there is a clear structural pathology in the nose or brain, treatment may be oriented toward the underlying lesion, such as functional endoscopic nasal surgery for chronic rhinosinusitis with polyps and neurosurgical interventions for a brain tumor.[3][8][9] In patients with damage to the olfactory epithelium and olfactory pathways due to inflammation, toxins, trauma, viral infection, or unknown causes, olfactory decline therapy may be difficult.[3][8][9]

Medications such as corticosteroids for chronic rhinosinusitis and other inflammatory conditions causing olfactory decline may be considered.[3][8] Other options may include sodium citrate, zinc, and vitamins, but their efficacy is not approved.[3][8] A non-surgical and non-pharmacological approach to improve olfactory functioning is olfactory training, where patients expose themselves twice daily to different odors over several months.[3][8] 

Several studies have reported on the efficacy of olfactory training.[10][11][12][13] However, these studies' findings were challenged for several reasons, such as the absence of an appropriate control group or the lack of placebo-controlled double-blinded protocols in these studies.[3][13] Moreover, some patients with olfactory dysfunction recover spontaneously. For instance, up to 20% of patients with post-traumatic olfactory dysfunction and up to 60% of patients with post-infectious olfactory dysfunction improve over the years spontaneously.[14][15] 

Additionally, patients of younger age, patients with a relatively well-preserved olfactory functioning, and patients with female gender and non-smokers have a good chance of a spontaneous improvement of olfactory functioning.[14] In any patient who uses tobacco, tobacco use should be discouraged as it is associated with diminished olfactory functioning and may support any attempt to improve olfactory functioning.[2] 

Olfactory training is comparatively simple, and, so far, serious side effects have not been reported. Although its precise mechanism of action and efficacy are incompletely understood, olfactory training is increasingly applied in routine care for patients with olfactory dysfunction due to different etiologies.[3][8][13]

Anatomy and Physiology

In comparison to other sensory systems, the olfactory system, including the olfactory epithelium and parts of the olfactory bulb, is unique in that it can adapt and regenerate.[16][17] Exposure to odors enhances this systemic process and leads to improved olfactory functioning.[18][19] This phenomenon was first discovered in healthy human subjects.[20][21] Later, repeated exposure to odors was also shown effective in patients with olfactory decline due to different etiologies.[22] Over the last 10 years, numerous studies have assessed the efficacy of olfactory training in humans.[10][11] Additionally, findings from several animal studies and functional imaging studies in humans support the effectiveness of olfactory training in olfactory recovery.[23][24][25][26]

Indications

Recent work suggests that olfactory training is more effective in younger individuals than the elderly and is more effective in individuals with severe olfactory dysfunction than in individuals who are only mildly affected.[27] However, olfactory training may be offered to treat olfactory dysfunction from different etiologies and irrespective of age and baseline olfactory functioning.[8][11][13][10] The most common indications reported in the literature are:[10][11][12][8][27]

  • Post-infectious olfactory dysfunction: It is one of the most common causes of an olfactory decline in clinical practice and one of the most common indications for olfactory training.[8][10][11] Following mild to severe upper respiratory tract infection, post-infectious olfactory dysfunction may occur. Olfactory testing in these patients shows diminished odor threshold and odor discrimination but normal odor identification.[28] Many patients with COVID-19 infection and decline of the chemical senses have this type of olfactory dysfunction.[29] The expectation of improving with olfactory training for patients with post-infectious olfactory dysfunction is comparatively good. A study involving more than 100 patients showed that 71% of patients with post-infectious olfactory dysfunction improve with olfactory training over 1 year while 37% of patients without olfactory training spontaneously recovered over the same period.[30] Abstinence from alcohol intake and gender do not impact the chance of improvement with olfactory training in patients with post-infectious olfactory dysfunction.[27] Olfactory training may be used in combination with corticosteroid treatment in selected patients with post-infectious olfactory dysfunction.[31][8][32] 
  • Post-traumatic olfactory dysfunction: This type of olfactory dysfunction may occur suddenly or with a delay after a brain or nasal injury.[8] Olfactory tests reveal diminished odor threshold and odor discrimination ability, while odor identification is normal.[28] Olfactory training has been reported to work for post-traumatic olfactory dysfunction [33][34][35][22][27], but effects may be smaller than for olfactory training in post-infectious olfactory dysfunction.[27] For instance, 23% of patients with post-traumatic olfactory dysfunction had improvement of their olfactory threshold when training with phenyl ethyl alcohol, while 5% of patients improved when training with mineral oil.[33]
  • Idiopathic olfactory dysfunction: The diagnosis is made after excluding all other causes of olfactory dysfunction.[8] In comparison to post-infectious olfactory dysfunction, the rate of success for improvement with olfactory training is less in patients with idiopathic olfactory dysfunction.[27]
  • Idiopathic Parkinson disease: Patients with idiopathic Parkinson’s disease have a severe impairment of their olfactory functioning, which starts many years before the onset of motor symptoms such as tremor, rigidity, and bradykinesic gait.[36][37][38] Olfactory testing typically shows impairment of odor discrimination and odor identification abilities, while the odor threshold is relatively normal.[28] Parkinson-medication does not improve olfactory functioning in patients with idiopathic Parkinson’s disease, and in light of the progressive, neurodegenerative process that underlies Parkinson’s disease, olfactory training may be an important treatment option for Parkinson patients who request treatment of their olfactory decline.[39] The success rate with olfactory training in patients with idiopathic Parkinson’s disease is lower than in patients with post-infectious olfactory dysfunction. About 20% of patients with idiopathic Parkinson’s disease benefit from olfactory training, while 10% recover spontaneously.[40]

Contraindications

There are no known contraindications for olfactory training in terms of past medical or surgical history or medications. However, the value of olfactory training for the treatment of olfactory dysfunction secondary to sinonasal disease needs to be determined.[8] 

Many patients with olfactory dysfunction secondary to sinonasal disease, especially those with chronic rhinosinusitis (with or without polyps), may benefit from functional endoscopic surgery.[9] Thus, surgical options may be considered first to manage patients with chronic rhinosinusitis with or without polyps.[8] Olfactory training may be considered for olfactory dysfunction secondary to sinonasal disease when surgical treatment options are exhausted, not possible, or after surgical interventions, as mentioned above.[9]

Equipment

The set-up for olfactory training includes four sniff bottles or jars (volume per bottle or per jar about 50 ml). Inside each bottle or jar is 1 ml of an odor soaked into cotton pads. The different scents are typically phenylethyl alcohol (rose scent), eucalyptol (eucalyptus scent), citronellal (lemon scent), and eugenol (clove scent­).[22] Olfactory treatment is an easy-to-use measure to improve olfactory dysfunction. It may be part of the therapeutic repertoire of both the specialized smell and taste clinic and the general ear, nose, and throat practice.[13]

Personnel

Patients need to be instructed on how to perform the olfactory training by a physician, a nurse, a nurse practitioner, or other medical assistance personnel, preferably with expertise in managing olfactory dysfunction.

Preparation

The cause of the olfactory dysfunction needs to be comprehensively determined following consensus guidelines.[8] Additionally, the patients must be counseled on the protocol typically applied for olfactory training. Beyond this, there is no preparation necessary for olfactory training.

Technique

For standard olfactory training, the patients sniff twice-daily (preferably once in the morning before breakfast and once in the evening before going to bed) for at least 20 to 30 seconds on each of the four scents separately. That means the patients do not simply sniff now and then on an odor. Patients who do olfactory training should focus on intensively sniffing the different odors following this rigid protocol.   

The odors for training are presented in sniff bottles or jars. Typically, patients do olfactory training for at least 24 weeks. In patients with post-infectious olfactory dysfunction, olfactory training over one year yielded better results than training over 16 weeks.[30] Another study showed that olfactory training with 12 odors was more effective than training with 4 odors in patients with post-infectious olfactory dysfunction.[41] A third study showed that high concentrations of odor were more effective than low concentrations of odor for olfactory training in patients with post-infectious olfactory dysfunction.[42] However, these observations had not been studied in patients with olfactory dysfunction due to other etiologies. For these patients, olfactory training following the standard protocol (that is, olfactory training with four different odors in standard concentrations twice daily for at least 24 weeks) may be a good starting point.

Olfactory training over several months is challenging for both the patients and the health care provider. The effects may be less than expected, and it takes a high degree of discipline to follow the standard protocol of olfactory training.[3][13] An olfactory training ball can be used to improve adherence and olfactory outcomes of olfactory training. The olfactory training ball has the size of a baseball, has four tubes containing the different tubes, and is light-weight and ergonomic.[43] Another approach to improving olfactory training adherence and outcomes is to call or schedule the patients for regular office visits (such as every 6 weeks) to monitor their adherence and progress.

Complications

Olfactory training has been assessed in more than 40 clinical studies, and results were reviewed in several independent meta-analyses.[10][11][12][32] None of the studies found complications arising from olfactory training. However, patients may experience olfactory testing as tiring because of the daily training session over several months.

Clinical Significance

Except for post-infectious olfactory dysfunction and olfactory dysfunction secondary to chronic rhinosinusitis, there is no established medical or surgical treatment for olfactory dysfunction.[8] Thus, olfactory training is the only treatment option for patients with olfactory dysfunction due to various etiologies. Therefore, olfactory training is of clinical significance in the management of patients with olfactory decline.

Enhancing Healthcare Team Outcomes

A multi-professional team is important for the best possible results of the olfactory training. This includes several members such as medical clerks, nurses, nurse practitioners, and physicians. Medical clerks are responsible for the coordination of the patient’s appointments and the ordering and storing of the supply needed for olfactory training.  Nurses and nurse practitioners must appropriately screen the patients to make sure they are good candidates for olfactory training. Additionally, they instruct the patients to ensure the patients properly perform the olfactory training procedure and thus, facilitate the best possible outcome of olfactory training. Furthermore, they also follow-up with the patient to ensure adherence to the protocol for olfactory training.

The clinicians oversee and supervise medical clerks, nurses, and nurse practitioners. Moreover, regular team conferences ensure that all team members are informed about all patients undertaking olfactory training, ensuring all patients' needs are addressed and resolved. Also, the team educates itself on the current development in the field of olfaction and olfactory training.


Article Details

Article Author

Martin Kronenbuerger

Article Editor:

Manfred Pilgramm

Updated:

12/24/2020 12:53:46 PM

PubMed Link:

Olfactory Training

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