What are the clinical manifestations of cytokine release syndrome?

Symptoms of Cytokine Release Syndrome

Cytokine release syndrome (CRS) is characterized by fever as the mandatory initial symptom, followed by a progressive constellation of manifestations including tachycardia, hypotension, hypoxia, nausea, headache, rash, shortness of breath, and in severe cases, respiratory failure, coagulopathy, and multiorgan system failure. 1

Core Clinical Manifestations

Constitutional Symptoms

• Fever ≥38°C - This is the defining and required symptom at onset 1, 2
• Headache
• Nausea
• Asthenia (weakness)

Cardiovascular Manifestations

• Tachycardia - occurs early in the syndrome
• Hypotension - ranges from mild (not requiring vasopressors) to severe requiring multiple vasopressors 2
• Capillary leak syndrome leading to hemodynamic instability 3

Respiratory Manifestations

• Tachypnea 1
• Shortness of breath/dyspnea 4
• Hypoxia - severity ranges from requiring low-flow nasal cannula to mechanical ventilation 2
• Respiratory failure in severe cases 1

Dermatologic Manifestations

• Rash 1, 4
• Scratchy throat 4

Severe/Life-Threatening Manifestations

• Coagulopathy 1
• Multiorgan system failure 1
• Hepatic dysfunction 5
• Encephalopathy 5

Temporal Pattern and Severity Grading

The onset of CRS is variable, with peaks typically occurring 2-7 days after CAR T-cell infusion, though delays up to 3 weeks have been reported 1. The symptoms are progressive in nature 1, meaning they can escalate from mild constitutional symptoms to life-threatening organ dysfunction.

Grading by Severity (ASTCT Consensus Criteria)

According to the European Society guidelines 2:

• Grade 1: Temperature ≥38°C without hypotension or hypoxia
• Grade 2: Temperature ≥38°C with hypotension not requiring vasopressors and/or hypoxia requiring low-flow oxygen (≤6 L/min)
• Grade 3: Temperature ≥38°C with hypotension requiring vasopressor support and/or hypoxia requiring high-flow oxygen or non-invasive ventilation
• Grade 4: Temperature ≥38°C with hypotension requiring multiple vasopressors and/or hypoxia requiring positive pressure ventilation (intubation)

Critical Clinical Pearls

High fever (38.9°C) and hemodynamic instability within 36 hours of CAR-T infusion predicts severe ICANS with high sensitivity 2, making early recognition of these symptoms crucial for preventing progression.

In patients with immune checkpoint inhibitors, longer time to fever onset, lower platelet count, and higher urea at presentation are associated with Grade 3-5 CRS 6, distinguishing this presentation from the more rapid onset seen with CAR-T therapy.

Common Pitfalls

• Do not dismiss isolated fever - fever is the mandatory first symptom and should trigger close monitoring for progression 1
• Recognize that symptoms can be mild initially - most patients experience mild to moderate symptoms that are easily managed, but rapid escalation can occur 4
• Be aware of localized presentations - CRS can present with organ-specific manifestations such as salivary gland swelling, particularly after tocilizumab administration 7
• Distinguish from infection - while fever is present, CRS is a sterile inflammatory process, though infection must always be ruled out 2

The pathophysiology involves supraphysiologic cytokine release from activated T cells and bystander immune cells, resulting in systemic inflammation that manifests across multiple organ systems 1. The severity correlates with T-cell activation levels and elevated cytokines, particularly IL-6 8, 3.