CRS stands for two different medical conditions depending on the context. Most commonly, it refers to chronic rhinosinusitis, a persistent inflammation of the sinuses affecting roughly 9% of the global population. In cancer treatment settings, CRS refers to cytokine release syndrome, a potentially serious immune reaction triggered by certain therapies. Both conditions involve inflammation, but they differ dramatically in cause, severity, and treatment.
Chronic Rhinosinusitis: The Most Common CRS
Chronic rhinosinusitis is long-term inflammation of the nose and the air-filled cavities (sinuses) surrounding it. To qualify as “chronic,” the inflammation must persist for at least 12 weeks. That’s the key distinction from a regular sinus infection, which typically clears up in days to a few weeks. CRS doesn’t just linger; it involves a sustained immune response in the sinus lining that can cycle between better and worse periods for months or years.
A formal diagnosis requires at least two of these symptoms: nasal congestion or obstruction, drainage from the nose (either forward or down the throat), reduced sense of smell, and facial pressure, pain, or fullness. Symptoms alone aren’t enough, though. A doctor also needs to confirm the inflammation visually, either through a scope inserted into the nose or through a CT scan showing thickened sinus tissue. Standard sinus X-rays aren’t reliable enough to make the call.
Two Types of Chronic Rhinosinusitis
CRS is split into two main forms based on whether soft, painless growths called nasal polyps are present. CRS with nasal polyps tends to be driven by a specific branch of the immune system that produces eosinophils, a type of white blood cell associated with allergic-type inflammation. This form is more likely to cause significant loss of smell and tends to be more difficult to control long-term. About 0.65% of the global population has this polyp-driven subtype.
CRS without nasal polyps is more variable in its underlying biology and doesn’t follow a single inflammatory pattern as neatly. Both forms cause overlapping symptoms like congestion and drainage, but treatments and long-term outlook can differ, which is why the distinction matters when your doctor is deciding on a management plan.
Who Gets Chronic Rhinosinusitis
The global prevalence of CRS sits at about 8.7%, making it one of the more common chronic conditions. Rates are higher in Europe than in North America, South America, or Asia. Several factors raise your risk: smoking, obesity, asthma, eczema, diabetes, and having a deviated nasal septum. Adults are affected more often than children.
Managing Chronic Rhinosinusitis
First-line treatment typically involves nasal saline irrigation (rinsing the sinuses with salt water) and corticosteroid nasal sprays to reduce inflammation. These two approaches form the backbone of CRS management for most people. For CRS with nasal polyps that doesn’t respond to standard treatment, newer biologic medications that target specific immune pathways have become an option. When medical therapy fails, sinus surgery to open blocked drainage pathways and remove polyps can provide relief, though polyps can recur over time.
CRS is a condition you manage rather than cure. Most people cycle through periods of good control and flare-ups, adjusting their treatment as needed.
Cytokine Release Syndrome: CRS in Cancer Treatment
The other CRS is cytokine release syndrome, a very different condition that occurs as a side effect of certain cancer immunotherapies. It happens most often after CAR-T cell therapy, a treatment where a patient’s own immune cells are engineered to attack cancer. When those modified cells encounter their target, they activate massively and trigger nearby immune cells and blood vessel cells to release a flood of signaling molecules called cytokines. Normally, cytokines coordinate the immune response in a controlled way. In CRS, the system overwhelms its own safety checks and produces what’s sometimes called a “cytokine storm.”
CRS onset typically occurs during the first week after CAR-T cell infusion, though the exact timing depends on the specific type of engineered cell used. Some constructs expand rapidly in the body and trigger symptoms sooner, while others grow more slowly and cause a delayed reaction.
Symptoms and Severity Grading
The hallmark symptoms of cytokine release syndrome are high fever, low blood pressure, low oxygen levels, and difficulty breathing. In more severe cases, it can affect multiple organs, including the liver, kidneys, heart, and nervous system.
Doctors grade CRS on a scale from 1 to 4:
- Grade 1: Mild symptoms like fever, managed with basic supportive care.
- Grade 2: Some signs of organ stress, requiring hospitalization and IV treatments but not intensive interventions.
- Grade 3: Low blood pressure needing IV fluids or blood pressure support, low oxygen requiring supplemental oxygen, or significant organ dysfunction.
- Grade 4: Life-threatening complications requiring mechanical ventilation or high-dose medications to maintain blood pressure.
The severity of CRS correlates with how much cancer is in the body at the time of treatment and how aggressively the engineered immune cells multiply. Patients with a higher disease burden tend to experience more intense reactions.
How Cytokine Release Syndrome Is Treated
The key breakthrough in managing CRS came from understanding that a signaling molecule called IL-6 plays a central role in driving the inflammatory cascade. The FDA has approved a medication that blocks IL-6 receptors specifically for treating severe or life-threatening CRS caused by CAR-T therapy. It’s given intravenously and can be repeated up to three additional times if the first dose doesn’t bring improvement, with at least eight hours between doses. Corticosteroids are used alongside it or on their own in milder cases.
Most patients recover fully from CRS when it’s caught and treated early. However, severe cases can cause prolonged organ dysfunction that persists even after cytokine levels return to normal. The potential complications, including heart dysfunction, respiratory distress, kidney or liver failure, and blood clotting problems, are why patients receiving CAR-T therapy are closely monitored in specialized centers during the days following infusion.