Dermatology World

Documenting Mohs surgery

Cracking the Code

Alexander Miller

Dr. Miller, who is in private practice in Yorba Linda, Calif., represents the American Academy of Dermatology on the AMA-CPT Advisory Committee.

By Alexander Miller, MD, September 2, 2013

You have just completed a three-stage Mohs surgical excision of a biopsy-proven recurrent morpheaform basal cell carcinoma located on a Medicare patient’s nose. You have documented a need for Mohs surgery based upon tumor location, histology, and recurrence, and you have specified in the patient’s record that clear margins were achieved after three stages of excision. Having measured and recorded the size of the surgical defect, you then confidently continue on to a reconstruction. Is your Mohs surgical documentation sufficiently complete to withstand a rigorous Medicare audit? 

Medicare contractors’ Mohs surgery Local Coverage Determinations (LCDs) vary in their wording. With varying amounts of detail, most require that the following information be documented in the operative report:

  1. Qualifying criteria for Mohs surgery (why Mohs surgery was chosen as the appropriate treatment).
  2. Who did the Mohs surgery; that is, that the physician was both the surgeon and pathologist.
  3. A description of the histology of the excised tumor. (This is currently required only by Palmetto and Noridian.)

Note that some Medicare Mohs LCDs include the following sentence relating to chart documentation:

“When the documentation does not meet the criteria for the service rendered or the documentation does not establish the medical necessity for the services, such services will be denied as not reasonable and necessary.” This should serve as an incentive for thorough documentation.


A 2013 CMS Medicare Learning Network Matters (MLN Matters®) article titled “Guidance to Reduce Mohs Surgery Reimbursement Issues” expands upon the language of some Mohs LCDs by specifying exact physical and documentation requirements for Mohs surgery. The publication provides the following documentation guidance and requirements: 

  1. The medical record should show that Mohs was chosen on the basis of any of the following:
    a. “Complexity” of the lesion: as in, poorly defined borders, suspected deep invasion, recurrence, prior irradiation
    b. Lesion size or location
    c. Maximum conservation of healthy tissue
    Only accepted diagnoses and indications, as listed in individual LCDs, will be considered for reimbursement. 
  2. Qualifications and Limitations of Coverage:
    a. The person performing the Mohs surgery must be a physician: MD or DO
    b. The physician must be skilled and trained in Mohs surgery and pathology interpretation
    c. The physician does both the surgery and the specimen interpretation
    (Significantly, an Office of the Inspector General (OIG) 2009 publication titled “Prevalence and Qualifications of Nonphysicians who Performed Medicare Physician Services,” which polled 250 physicians, found instances of unqualified medical assistants performing Mohs surgical excisions. Beyond the questions of qualifications and the legality of having medical assistants doing surgery is the fact that Medicare specifically directs that only physicians must do Mohs surgery on Medicare patients. The entire OIG report may be perused at
  3. Operative documentation should note:
    a. Evidence that the same physician acted as the surgeon and pathologist
    b. Location, number, and size of the lesions
    c. Number of stages performed
    d. Number of specimens per stage 
  4. Histology documentation must include:
    a. First stage:
        i. Depth of invasion
        ii. Pathological pattern of the tumor
        iii. Cell morphology
        iv. If present, note perineural invasion or scar tissue
    b. Subsequent stages:
        i. If tumor characteristics are the same as in the first stage, note this fact only
        ii. If tumor characteristics are different from the first stage, describe the differences
The MLN Matters article specifically spells out how billing should be done for Mohs surgery carried over from one day into another: “If MMS on a single site cannot be completed on the same day because the patient could not tolerate further surgery and the additional stages were completed the following day, you must start with the primary code (CPT code 17311) on day two. Computer edits will reject claims where a secondary code (e.g., CPT code 17312) is billed without the primary code (e.g., CPT code 17311) also appearing on same date of service, and the same claim.” Medicare would like the Mohs billing series to start all over, with the primary code, 17311 or 17313, when Mohs is continued on a subsequent day.
The entire text of the MLN Matters “Guidance to Reduce Mohs Surgery Reimbursement Issues” may be accessed at:

The Mohs LCDs all contain the following billing guidelines dealing with lesions biopsied on the same day as Mohs surgery is done:

a. If a different lesion is biopsied on the same day as Mohs, append a 59 modifier to the biopsy code and clearly document that a separate lesion was biopsied. Specifying this in the “Notes” section of the billing may also help with avoiding denial of payment.

b. Medicare will pay for a confirmatory biopsy of the lesion excised with Mohs surgery only in the following cases:i. If a biopsy had not been done in the previous 60 daysii. Or if, despite reasonable effort, the results of a recent biopsy were unobtainable

In some select instances there is a valid medical care reason for sending out some of the excised tissue for formalin-fixed histopathologic evaluation by an outside lab. This is not strictly prohibited by the Mohs LCDs and the MLN publication, but such a practice may trigger a Medicare Recovery Audit Contractor (RAC) audit or a non-payment for the surgery or a demand for a refund. The RAC Contractors are actively monitoring Mohs surgery when pathology is billed by different provider. All RAC contractors have been instructed to monitor and review Mohs claims when either surgery or pathology is delegated to another physician who reports services separately. To view active RAC issues, visit

One should be prepared to appeal such a decision by submitting a valid medical reason for sending out the tissue for an outside evaluation, and by referring to the AAD “Position Statement on Appropriate Uses of Paraffin Sections in Association with Mohs Micrographic Surgery,” available on the AAD website at

So, what is the practical outcome of all of the above requirements? It is simple: if they are not all fulfilled to the Medicare contractor’s satisfaction, your perfectly reasonable and appropriate Mohs surgery may be denied upon audit.

Example 1: A patient is referred to you and travels a long distance to have a Mohs surgical excision of a broad suspected basal cell carcinoma located on his nose. As no biopsy had been done on the lesion, you decide to do both the biopsy and the Mohs surgery on the same day. You confirm the presence of an infiltrating basal cell carcinoma with a biopsy processed as a frozen section and read out by you, and then proceed to excise the tumor with two stages of Mohs surgery. You bill:
  • 11100-59 for the biopsy;
  • 88331-59 for the frozen section; and
  • 17311 and 17312 for the Mohs surgery.
Answer: Correct. Since no prior biopsy has been done, a preoperative biopsy is both medically appropriate and Medicare reimbursable. The biopsy and the frozen section tissue processing with interpretation are billed with a 59 modifier in order to distinguish them from the Mohs surgery. While a permanent section may be required for the biopsy and should be able to withstand an audit, a permanent section for the last stage of Mohs should only be ordered for a specific lesion and may raise an audit flag.
Example 2: You have a busy two-Mohs-surgeon practice. You excise a squamous cell carcinoma from an ear with two stages of Mohs surgery. As after each excision stage you were occupied with a reconstruction procedure on another patient, your colleague Mohs surgeon read out your patient’s slides. 
You then bill 17311 and 17312 for the Mohs surgery.
Answer: Incorrect. Although your colleague is a Mohs surgeon, you yourself did not both personally excise your patient’s tissue and perform the histopathologic interpretation of that tissue. Consequently, since the same person did not act as both the surgeon and the pathologist, Mohs surgery may not be billed. 
Example 3: You schedule multiple Mohs surgeries in the morning and, for the sake of moving your elderly patients along, have your trained physician assistant excise Mohs layers on select patients. You then do the histopathology slide interpretation and bill for the Mohs surgeries with the appropriate 173xx series of codes.
Answer: Incorrect. Medicare guidelines specify that both the excision and the histopathology interpretation must be done by a physician MD or DO.