"What Causes Chronic Sinusitis?"

By Daniel Larson, MD

Chronic Rhinosinusitis (CRS) is a complex group of conditions that cause persistent inflammation of the nasal sinuses. This inflammation in turn can lead to nasal congestion, thick drainage and decreased sense of smell/taste. In addition, patients who suffer from CRS are more prone to recurrent sinus infections requiring antibiotics.

It is important to remember that CRS does not have a single cause, but multiple causes. Each patient’s case is unique. In this article we will cover the most common subtypes of Chronic Rhinosinusitis and their causes.

1. Non eosinophilic sinusitis

In studies of US patients with chronic sinusitis, non eosinophilic sinusitis is the most common subtype. This form of sinusitis most likely arises from an underlying anatomic obstruction of the nasal sinuses, which prevents proper mucous drainage and airflow. This leads to chronic inflammation and makes patients prone to recurrent infections.

An alternative cause may be from the formation of bacterial biofilms which can cause bacterial sinus infections that do not clear with oral antibiotics.

2. Eosinophilic Sinusitis

This more severe form of sinusitis is typically found in patients with Asthma or other chronic inflammatory conditions that cause an increased number of eosinophils (a type of inflammatory white blood cell) to be present in sinus tissues. In the same way that Asthma is a disease where the lungs are more sensitive to certain conditions, Eosinophilic sinusitis is a condition where the lining of the sinuses is more sensitive and prone to strong inflammatory responses.

Patients with this form of CRS are more prone to the formation of nasal polyps. Nasal polyps are very swollen bags of tissue that develop in the sinuses and can cause severe blockage.

3. Allergic Fungal Sinusitis (AFS)

This form of sinusitis can account for 5-10% of all cases of chronic sinusitis that require surgery to repair. AFS can cause severe symptoms that are usually limited to one side of the sinuses. It is caused by an abnormally strong allergic/eosinophilic response to common forms of fungus that are present in the environment. AFS is not a fungal infection and does not improve with antifungal medications. It is one of the forms of sinusitis that only improves significantly with surgery to open the affected sinus(es) and wash out the offending fungal elements.

4. Aspirin Exacerbated Respiratory Disease (AERD)

AERD, also known as "Sampter's Triad" is a very severe form of chronic sinusitis where patients suffer from poorly controlled Asthma and severe sinusitis that is made worse by taking aspirin or other NSAID medications such as ibuprofen. This form of sinusitis may account for up to 30% of cases of CRS in patients with Asthma. Due to the underlying inflammatory condition in AERD, patients are prone to recurrent polyp formation, even after surgery. Long term medical care including aspirin desensitization or biologic medications may be required.

5. Odontogenic sinusitis

This surprisingly common form of chronic sinusitis is due to a tooth infection (typically one of the upper molars) that has spread through the tooth root into the sinuses. It usually affects one side of the sinuses only and can be very difficult, if not impossible, to clear with antibiotics alone. An evaluation by a dentist or oral surgeon is necessary to determine if the affected tooth needs to be removed as well.

6. Cystic Fibrosis (CF) related CRS

Children and adults with cystic fibrosis are prone to a very severe form of chronic sinusitis that can develop at a very young age. This can lead not only to severe nasal blockage, but also make patients prone to chronic infections which can worsen their lung function.

7. Chronic sinusitis in immunosuppressed patients

This subtype of chronic sinusitis is increasing in prevalence due to the increasing number of patients treated with medications that decrease immune function (eg. HumiraⓇ for arthritis). These patients are prone to chronic infections and the formation of antibiotic resistance biofilms due to a weakened immune system. In addition to surgery to clear the infection, many patients require daily nasal washes to control the growth of biofilms.

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