Pathology/Lab Coding Alert

Question: Should I use C4A.39 for Merkel cell carcinoma found only on the scalp, since C4A.4 states “scalp and neck”?

Minnesota Subscriber

Answer: No, C4A.39 (Merkel cell carcinoma of other parts of face) does not apply to the scalp. Although the forehead is part of the face, the scalp begins on the upper edge of the forehead at the “hairline.” In cases of male-pattern baldness, the differentiation of forehead and scalp is still evident because specific musculature allows the patient to wrinkle or furrow the forehead but not the scalp.

The correct code for Merkel cell carcinoma of scalp is C4A.4 (Merkel cell carcinoma of scalp and neck). Use this code for scalp and/or neck Merkel cell carcinoma. Remember that “and” in ICD-10-CM means “and/or.”

Tip: Don’t be confused by the letter “A” in the 3rd position of the code, C4A.-. Although all ICD-10-CM codes initially began with an alpha character in the first position, followed by numeric second, third and fourth characters, updates to the code set has resulted in a letter in the third position when all digits 0-9 are already in use for that code family. You’ll find the anomalous codes inserted between appropriate numeric codes within the family. In that way, C4A lies between families C43 (Malignant melanoma of skin) and C44 (Other and unspecified malignant neoplasm of skin).