ICD-10-CM > S00-T88 > T20-T25 > T23 > T23.4 > T23.42 > T23.421 T23.421 Corrosion of unspecified degree of single right finger (nail) except thumb Non-Billable/Non-Specific Codes T23.421A..., initial encounterT23.421D..., subsequent encounterT23.421S..., sequela