C4A.21 (Merkel cell carcinoma of right ear and external auricular canal) compared with C4A.22 (Merkel cell carcinoma of left ear and external auricular canal), from the official CMS tabular data. C4A.21 and C4A.22 code the same condition on opposite sides. MedCoder-derived
Same condition; these differ only in which side is documented.
These codes share a category and title and differ only in the side affected. The documentation decides which applies, and a bilateral code is reported only where the code set provides one.
Source: ICD-10-CM tabular list (laterality variant derived from the code title)
Same condition, opposite side. C4A.21 and C4A.22 name the same condition on opposite sides of the body.
Same category and title, differing only in which side is affected — the documentation decides which one applies, and a bilateral code is reported only where the code set provides one.
| C4A.21Merkel cell carcinoma of right ear and external auricular canal | C4A.22Merkel cell carcinoma of left ear and external auricular canal | |
|---|---|---|
| Billing status | Billable | Billable |
| Classification | C00-D49 — Neoplasms (C00-D49) | C00-D49 — Neoplasms (C00-D49) |
| Definition | Merkel cell carcinoma of right ear and external auricular canal is a billable ICD-10-CM diagnosis code (C4A.21). | Merkel cell carcinoma of left ear and external auricular canal is a billable ICD-10-CM diagnosis code (C4A.22). |
Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources