ICD-10-CM > S00-T88 > T20-T25 > T21 > T21.5 > T21.55 T21.55 Corrosion of first degree of buttock Non-Billable/Non-Specific Applicable To Corrosion of first degree of anus Codes T21.55XA..., initial encounterT21.55XD..., subsequent encounterT21.55XS..., sequela