Mohs and 'slow Mohs'

Cracking the Code

Dirk Elston

Dr. Elston, who serves as director of the Ackerman Academy of Dermatopathology in New York, has served on the AMA-CPT Advisory Committee.

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I’ve just started to perform “slow Mohs” with immunostains for lentigo maligna. My dermatopathologist reads the sections for me, and is able to process the immunostains and report the results within a couple of hours. Today I removed a lentigo maligna in three stages and closed it with a flap. Do I report this as Mohs?

Answer: No. Mohs requires that the surgeon also serve as the pathologist. If your pathologist reads the slides, it’s not Mohs. For billing purposes, this procedure is considered a staged excision with the pathology services reported separately by the pathologist. If all of the stages are accomplished on the same day, an excision would be reported as a single excision of a malignant lesion with the final diameter reported as the excised diameter. In this case, there was an adjacent tissue transfer as well. If this is performed on the same day as the excision, the excision of the malignant lesion is included in the adjacent tissue transfer code and cannot be reported separately. So the only code that would be reported by the surgeon on this date of service (DOS) would be the adjacent tissue transfer. Per AMA/CPT 2011, the adjacent tissue transfer code descriptor states that “The excision of a benign lesion (11400 11446) or a malignant lesion (11600 11646) is not separately reportable with codes 14000-14302.” (Although you and I know what we mean by “slow Mohs” and I will use the term in this article, I suggest that you avoid the term in the medical record, as it will confuse auditors. Instead, refer to the procedure as excision with margin control.)

If “slow Mohs” stages take more than one day to perform, the final excised diameter would be reported on the first day, and the additional margin diameter would be reported on the second day with a 58 modifier indicating that this procedure was staged. True Mohs surgery has a zero-day global period, but “slow Mohs” reported as excision of a malignant lesion has a 10-day global period. An adjacent tissue transfer has a 90-day global period (and includes excision of the malignant lesion if performed on the same DOS).[pagebreak]

If a complex closure was required, rather than an adjacent tissue transfer, the lesser valued code would be subject to multiple surgery reduction if the two procedures are performed on the same DOS. True Mohs is no longer exempt from the 51 modifier, and hence subject to the multiple surgery reduction rule when performed on the same day as the closure.

The official AADA position statement on Appropriate Uses of Paraffin Sections in Association with Mohs Micrographic Surgery (approved by the Board of Directors Aug. 1) lists the following as examples that may justify appropriate use of a second opinion from a pathologist:

  • (1) A second opinion consultation is required during surgical treatment of melanoma.
  • (2) Further tissue processing is required to assess features of an aggressive, deep, or histologically unusual tumor.
  • (3) Paraffin section evaluation is used to confirm a diagnosis other than what was found on a prior pathology report, upon which Mohs surgery was done.
  • (4) Further tissue analysis is necessary to complete the staging of a tumor so that the need for additional therapy, such as radiation or chemotherapy, can be determined.
  • (5) Unusual findings during frozen section evaluation, or during other portions of the Mohs case, lead the physician to conclude that a second pathologic opinion is necessary.
  • (6) Despite proper processing technique, frozen section interpretation is not sufficient to assess the tissue margin with a high degree of reliability.
  • (7) A biopsy specimen of tumor not previously biopsied is obtained and assessed by frozen section immediately before commencement of Mohs; the pathologic diagnosis is then confirmed by paraffin section.

The AADA position statement also provides guidance as to when the criteria for Mohs surgery are not met. The position statement notes that “In general, this occurs when one or more of the tasks that must be performed by the operating surgeon are delegated to another physician.” Examples include:

  • (1) When all specimens removed during the course of the procedure are sent to a pathologist for interpretation of paraffin sections, then Mohs is no longer being performed. Instead, the physician removing the tissue should characterize that process as an excision and document it as such.
  • (2) When a separate physician, such as a pathologist, reads all the slides made from tissue removed by the physician during a particular stage, this will constitute “delegation of responsibility” and as such, makes the stage incompatible with Mohs surgery. This differs from the permissible case where, during a particular stage of Mohs surgery, the physician obtains and processes all the tissue, and reads all of the slides for margin assessment, but then obtains additional second opinion pathologic consultation on a portion of these slides.

The position statement notes that “Routine review of histopathlogic features of a tumor being treated with Mohs by a pathologist is not compatible with Mohs surgery. In general, pathologic consultation should occur in a rare number of cases.”[pagebreak]

Example 1: You remove a large dermatofibrosarcoma protuberans from the chest, layer by layer, using frozen sections with you acting as the pathologist. The final stage you examined yourself was equivocal, so you take an additional layer and send it to a pathologist for immunostaining. The pathologist reports clear margins the next day and you perform an adjacent tissue transfer.

All services performed were medically necessary and prudent. In rare instances, it may be appropriate (before, during, or after the Mohs procedure) to send tissue for paraffin sections to a separate pathologist. This does not preclude reporting the Mohs surgery for the prior stages where you acted as both surgeon and pathologist. It may also be appropriate for you to bill a staged excision reporting the diameter of the final additional margin that was sent to a separate pathologist as well as the adjacent tissue transfer on the subsequent day. Your documentation must succinctly indicate the reason the additional layer was submitted to the pathologist to document medical necessity in the interest of good patient care. The documentation should be clear and unequivocal, as it will be important in the event of an audit. The pathologist would bill separately for his or her services.

Example 2: You remove a large lentigo maligna from the face, layer by layer. The sections are sent to a separate lab where they are read by a pathologist who is an expert in interpreting pigmented lesion margins. At the end of the same day, you close the wound with an adjacent tissue transfer.

You did not serve as both the surgeon and pathologist, so this should not be reported as Mohs. You report the adjacent tissue transfer. The staged excision is included in the payment for the adjacent tissue transfer and cannot be reported separately. The pathologist should bill for his or her professional services.

The full position statement on Appropriate Uses of Paraffin Sections in Association with Mohs Micrographic Surgery is available online at