Code G92, Toxic encephalopathy, has been expanded based on the American Society for Transplantation and Cellular Therapy (ASTCT) scale. This expansion also includes codes that describe other and unspecified toxic encephalopathy. The new codes are as follows:
- G92.00, Immune effector cell-associated neurotoxicity syndrome, grade unspecified
- G92.01, Immune effector cell-associated neurotoxicity syndrome, grade 1
- G92.02, Immune effector cell-associated neurotoxicity syndrome, grade 2
- G92.03, Immune effector cell-associated neurotoxicity syndrome, grade 3
- G92.04, Immune effector cell-associated neurotoxicity syndrome, grade 4
- G92.05, Immune effector cell-associated neurotoxicity syndrome, grade 5
- G92.8, Other toxic encephalopathy
- G92.9, Unspecified toxic encephalopathy.
ICANS can occur with or independently of cytokine release syndrome (CRS), another condition that is associated with CAR T-cell therapy. Symptoms usually occur within 1-3 weeks after CAR T-cell infusion. They include expressive aphasia, impairments of attention, changes in handwriting, tremor, motor weakness, and lethargy that can progress to global aphasia, seizures, a depressed level of consciousness, and in rare cases, cerebral edema.
In 2018, the ASTCT developed a consensus grading for ICANS. Factors such as an immune effector cell encephalopathy (ICE) score, along with an evaluation for level of consciousness, seizure activity, motor findings, and elevated intracranial pressure/cerebral edema determine the ASTCT ICANS grade according to the most severe event (not attributable to any other cause). For example, a patient with grade 4 ICANS indicates at least one of the following as the most severe event: being unarousable or requiring vigorous or repetitive tactile stimuli; prolonged, repetitive seizures or electrical seizures without return to baseline in between; deep focal motor weakness such as hemiparesis or paraparesis; or diffuse cerebral edema on neuroimaging. A patient with grade 2 ICANS awakens to voice, and is without seizure activity, motor findings or intracranial pressure/cerebral edema.
These new codes should only be assigned based on explicit documentation by the provider of the ICANS grade; otherwise, assign the code for unspecified grade. The underlying cause of ICANS is coded first. Code also any associated signs and symptoms, such as seizures and cerebral edema.