Loss of sense of smell

Most people with Parkinson’s report losing their sense of smell years or even decades prior to diagnosis.

Diminished and loss of sense of smell can impact quality of life affecting taste and, in some cases, leading to weight loss.

Ironically, there has been recent research into the odour people with Parkinson’s have as a potential way to detect the condition.

Smell & Parkinson’s

Many conditions can cause reduced ability to detect odours or complete loss of your sense of smell. This loss could be temporary or lasting. Lasting can be an indicator for brain disease, including a very early symptom of Parkinson’s. However not all people with a reduced sense of smell will go on to develop Parkinson’s.

Scientists do not know why smell loss occurs in Parkinson’s. One popular theory is that the Parkinson’s process may start in gut and the part of the brain controls sense of smell.

What is hyposmia?

Most people don’t realise they have a reduced or lost sense of smell (hyposmia and anosmia respectively) until they are tested. All major brain disorders (e.g. MS, PD, ALS, Alzheimer’s, Huntington’s) are associated with smell loss.

Common symptoms that indicate hyposmia include having a hard time identifying smells, not being able to smell as well as you used to, a noticeable educed sense of taste, and/or nasal congestion and swelling. Anosmia is complete loss of the sense of smell.

Hyposmia is one of the most common and best-characterised conditions that is also one of the first non-motor features of Parkinson’s. The association of hyposmia with Parkinson’s is widely accepted; however the likelihood of developing Parkinson’s is unclear (1).

Other Causes of Smell Loss

About half of people over age 60 lived with some loss of sense of smell. Parkinson’s is not the only condition that can cause this. Other causes can include:

COVID-19
Nasal congestion, cold, allergies, or viral infection
Head injury
Aging
Nasal polyps (growths inside the nose or sinuses)
Lack of zinc

Managing Loss of Sense of Smell

Our sense of taste is inexorably linked to our sense of smell. Loss or diminished sense of small impacts quality of life by reducing appetite and lowering our enjoyment of food.

However, there are not many treatments for lost sense of smell. You can seek advice about maintaining your enjoyment of foods through varied textures and with a dietician or nutritionist.

What Should I Do?

Make sure you have fire alarms and smoke alarms in your home. Write dates on leftovers and read best before labels to ensure food safety.

Consult a dietician/nutritionist to ensure you are still eating enjoyably and maintaining your optimal nutrition and weight.

Your Care

An ear, nose, and throat specialist (ENT) can do some tests to see how well you can smell. You may need additional tests to rule out other causes of your symptoms.

If you or someone you know has trouble smelling foods like bananas, dill pickles or liquorice, ask your GP about being assessed for other early Parkinson’s symptoms.

Early detection of changes in the brain is important as this can help scientists understand the causes of Parkinson’s and develop better treatments, including neuroprotective strategies which aim to slow or prevent the development of the condition.

To maximise the potential of such strategies they need to begin as early as possible in the course of the disease, so a reliable smell test could be invaluable in contributing to early diagnosis and prompt neuroprotective treatment.

Your body odour as an indicator of Parkinson’s

There are currently no tests that can diagnose Parkinson’s. A collection of your history and clinical examination by a GP, geriatrician, or neurologist. Having a definitive biomarker to objectively make a diagnosis would simplify the process and ensure early and accurate diagnoses.

A retired Scottish nurse named Joy Milne noticed her husband’s odour change years prior to his diagnosis. It was only after attending Parkinson’s-related events after his diagnosis that she noticed a similar odour on every person she met with Parkinson’s.

People with Parkinson’s often have patches of scaly, red skin on the face and scalp due to over-active glands that secrete an oily, waxy substance called sebum resulting in seborrheic dermatitis.

Diagnosis of Parkinson’s by taking a swab of the extra sebum that produces the odour is being seriously investigated as a non-invasive biomarker, just like high blood pressure can indicate heart problems.

Joy brought this to the attention of researchers who then ‘tested’ her overly sensitive nose and she proved there was something more to this casual observation.

Remember, in order for this biomarker to be useful, it must be able to detect Parkinson’s earlier and more accurately than traditional clinical examination, be an affordable option, is able to be done anywhere, and be easily collected and examined.

The good news is current research by a lab in the UK is pointing towards a 3-minute test to examine sebum for certain Parkinson’s biomarkers.

Refer to the Symptoms of Parkinson’s factsheet to learn about other symptoms that point towards an early Parkinson’s diagnosis.

Infosheet under review

References:

(1) Sui, X., Zhou, C., Li, J., Chen, L., Yang, X., & Li, F. (2019). Hyposmia as a Predictive Marker of Parkinson’s Disease: A Systematic Review and Meta-Analysis. BioMed research international, 2019, 3753786. https://doi.org/10.1155/2019/3753786