CRS most commonly stands for chronic rhinosinusitis, a persistent inflammation of the sinuses and nasal passages lasting at least 12 weeks. It affects roughly 9% of the global population, making it one of the most widespread chronic conditions. In oncology settings, CRS can also refer to cytokine release syndrome, a serious inflammatory reaction to certain cancer immunotherapies. This article covers both conditions so you can identify which one applies to you.
Chronic Rhinosinusitis: The Basics
Chronic rhinosinusitis is inflammation of the lining inside your nose and the hollow spaces (sinuses) behind your cheeks, forehead, and eyes. Unlike a regular sinus infection that clears up in a few weeks, CRS persists for at least three months. It causes a combination of congestion, facial pressure, thick nasal discharge, and reduced sense of smell that doesn’t fully resolve between flare-ups.
To be diagnosed, you need at least two of those ongoing symptoms plus visible evidence of inflammation. That evidence comes from either a small camera passed into the nose (nasal endoscopy) showing polyps, swelling, or pus, or a CT scan showing thickened sinus membranes. This combination of symptoms and objective findings is what separates CRS from allergies or recurring short-term infections.
CRS is more common in Europe than in North America or Asia, though it occurs worldwide. It’s not life-threatening, but it significantly affects daily quality of life: breathing, sleep, energy levels, and the ability to taste and smell food.
Two Main Types of CRS
Doctors divide chronic rhinosinusitis into two categories based on whether nasal polyps are present.
CRS without nasal polyps (CRSsNP) is the more variable form. The inflammation can be driven by different immune pathways, and the symptoms tend to center on congestion, facial pain, and discolored nasal drainage. Treatment typically focuses on saline rinses and steroid nasal sprays. Oral steroids are generally reserved for cases where doctors suspect a specific pattern of immune-driven inflammation.
CRS with nasal polyps (CRSwNP) involves soft, painless growths that develop on the sinus lining. These polyps are driven by a particular branch of the immune system that produces high levels of certain white blood cells called eosinophils. Loss of smell is especially prominent in this type. The global prevalence of the nasal polyp form is lower, around 0.65%, but it tends to be more difficult to control. Treatment includes steroid sprays, saline irrigation, short courses of oral steroids, and in severe cases, injectable biologic medications that target the underlying immune overreaction.
How CRS Is Treated
Most people start with a combination of daily saline nasal rinses and corticosteroid nasal sprays. Saline rinses physically flush out mucus and inflammatory debris, while steroid sprays reduce the swelling that blocks sinus drainage. For many people, this is enough to keep symptoms manageable.
When medical treatment alone isn’t sufficient, functional endoscopic sinus surgery (FESS) is the standard surgical option. The procedure opens blocked sinus drainage pathways using small instruments passed through the nostrils, with no external incisions. Studies consistently show strong results: around 86 to 87% of patients report significant symptom improvement after surgery, and roughly 72 to 78% report meaningful improvement in overall quality of life. Quality of life scores tend to improve most dramatically in the first month after surgery and remain stable through at least a year of follow-up.
Recurrence is the main concern. Some studies report recurrence rates as low as 6%, while others tracking patients over nine months found rates closer to 31%, likely reflecting differences in the severity of disease being studied and how recurrence was measured. The nasal polyp form is more prone to coming back.
For people with severe nasal polyps that keep returning despite surgery and steroids, the FDA has approved dupilumab, an injectable biologic. In a 52-week study, dupilumab significantly reduced sinus inflammation on CT scans, shrank nasal polyps, improved congestion and sense of smell, and cut the need for additional surgeries and oral steroids. It’s approved for adults and children aged 6 and older. Common side effects include injection-site reactions, elevated white blood cell counts, insomnia, toothache, stomach irritation, and joint pain.
How CRS Differs From Allergies or Acute Sinusitis
Allergic rhinitis and CRS share symptoms like congestion and runny nose, but allergies typically cause itchy eyes and sneezing, which aren’t hallmarks of CRS. Allergies also tend to follow seasonal patterns or clear triggers like pet dander, while CRS symptoms are present most of the time regardless of allergen exposure.
Acute sinusitis, the kind that follows a cold, resolves within a few weeks. If your symptoms persist beyond 12 weeks with no real breaks, that timeline alone points toward CRS. A CT scan can help confirm the diagnosis by showing persistent sinus opacification, thickened membranes, polyps, or blockage of the narrow drainage channels. CT imaging also helps rule out more serious causes like tumors or structural abnormalities in the bones separating the sinuses from the brain and eye sockets.
Cytokine Release Syndrome: The Other CRS
In cancer treatment, CRS refers to cytokine release syndrome, a very different condition. This is a systemic inflammatory reaction triggered when certain immunotherapy drugs activate the immune system so powerfully that it floods the body with signaling molecules called cytokines. It was first described in the early 1990s with the introduction of an immune-suppressing drug used in organ transplantation, but it has become most clinically relevant with the rise of CAR-T cell therapy and bispecific antibody treatments for blood cancers.
When CAR-T cells or bispecific antibodies bind to their targets on cancer cells, they also activate surrounding immune cells and even blood vessel lining cells, triggering a massive cytokine release. CRS is the most common serious side effect of these therapies.
Symptoms and Severity of Cytokine Release Syndrome
The hallmark of cytokine release syndrome is fever, defined as a temperature of 38°C (100.4°F) or higher that isn’t explained by an infection. Mild cases (Grade 1) involve only fever. As severity increases, blood pressure drops and oxygen levels fall.
- Grade 1: Fever only, no blood pressure or oxygen problems.
- Grade 2: Fever with low blood pressure that responds to fluids alone, or a need for supplemental oxygen at low flow rates.
- Grade 3: Blood pressure drops enough to require medications to maintain it, or oxygen needs escalate to high-flow delivery systems or face masks.
- Grade 4: Multiple blood pressure medications are needed, or the patient requires mechanical breathing support.
Severity is determined by whichever is worse: the blood pressure drop or the oxygen deficit. Once anti-inflammatory treatment is given and fever resolves, grading shifts to rely on blood pressure and oxygen status alone.
How Cytokine Release Syndrome Is Managed
Mild CRS often resolves with supportive care like fluids and fever-reducing medications. For more severe cases, the standard treatment is an intravenous infusion of a drug that blocks one of the key cytokines driving the reaction. This medication can be repeated up to three additional times if symptoms don’t improve, with at least eight hours between doses. Steroids may be added alongside. Most patients recover fully, and the occurrence of CRS doesn’t necessarily mean the cancer therapy has failed. In fact, some degree of immune activation is expected with these treatments.
If you’ve encountered the term “CRS disease” in the context of a cancer treatment plan, your oncology team will be monitoring for it from the moment therapy begins. Grade 1 and 2 cases are the most common and typically resolve within days.