Indications

MMS is often indicated for NMSCs at high risk for local recurrence or possible significant functional or cosmetic impairment. Clinical morphology, anatomic location and size, histology (including level of invasion), patient immunity, and recurrence after previous treatment are criteria that can be used to determine the appropriate use of MMS for treating a cutaneous neoplasm. The indications for MMS, as outlined in the clinical guidelines currently adapted by Medicare for reimbursement include the following:

• 1.
  

  BCC in anatomic locations where they are prone to recur including the mask area of the face that are mainly embryonic fusion planes (central face, eyelids, eyebrows, periorbital areas, nose, lips, chin, mandible, periauricular areas, ear, temple), scalp, forehead, cheeks, and neck, genitalia, hands, and feet

  
  
• 2.
  

  NMSCs that have 1 or more of the following features: recurrent or positive margin on recent excision; aggressive pathology in the hands and feet, genitalia, and nail unit/periungual; large size (2.0 cm or greater); poorly defined borders; age less than 40 years; radiation-induced; immunocompromised host; arising in an old scar (eg, a Marjolin ulcer); associated with xeroderma pigmentosum; deeply infiltrating lesion or difficulty estimating depth of lesion; perineural invasion on biopsy

  
  
• 3.
  

  SCCs showing any of the following: undifferentiated to poorly differentiated, adenoid (acantholytic), adenosquamous, desmoplastic, infiltrative, perineural, periadnexal, or perivascular, and verrucous; subtypes including Bowen disease (BCC in situ), erythroplasia of Queryrat, and verrucous carcinoma; although tumors treated with excision have a cure rate of 80%, the reported cure rate with Mohs surgery approaches 98%

  
  
• 4.
  

  Basal cell nevus syndrome

  
  
• 5.
  

  Other cutaneous neoplasms: aside from BCCs and SCC, MMS can successfully treat a variety of cutaneous tumors, as outlined later. Although its use and application is clear in most instances, its use for the some tumors is controversial because of tumor characteristics (multifocality, discontinuous growth patterns) or technique limitations (inherent disadvantages of frozen sections vs permanent sections).

Utilization

Mohs surgery is performed on more than 876,000 tumors per year in the United States and that rate is rapidly increasing. Approximately half of all MMS cases are performed on Medicare beneficiaries. Analysis of Medicare claims data can therefore yield useful information on time trends in MMS utilization. Although a few NMSCs in the Medicare population are treated with MMS, its utilization is increasing at a faster rate than the use of other treatment modalities, such as excision. The rate of Mohs surgery per 1000 Medicare beneficiaries increased by 236% between 1999 and 2009, whereas excisions and destructions of lesions increased by approximately 20%. It is unclear to what extent the increasing rate of Mohs surgery utilization is because of the epidemic increase in the incidence of NMSC over time, and to the increasing availability of Mohs surgeons, who were in short supply until 10 to 20 years ago. It has been suggested that previous lower utilization rates were associated with a lack of availability of Mohs surgery services. Mohs surgery was more likely than surgical excision on the face and less likely elsewhere. Tumor location was associated with MMS utilization, with 47% of facial lesions and 15% of lesions on the rest of the body treated with MMS. Patient age, race, and geographic region were also significantly associated with the likelihood of Mohs surgery. The use of Mohs for these cancers decreased with patient age (from 41% of patients aged 67 to 69 years to 34% of patients 85 years or older). Mohs was used in 37% of white patients, 23% of black patients, and 29% of patients of other races. Areas with high densities of Mohs surgeons were likely to have higher rates of MMS; however, some areas with low densities still had high rates of Mohs utilization. There was wide variation in regional MMS utilization and geographic disparity that warrants further investigation.

Utilization

Mohs surgery is performed on more than 876,000 tumors per year in the United States and that rate is rapidly increasing. Approximately half of all MMS cases are performed on Medicare beneficiaries. Analysis of Medicare claims data can therefore yield useful information on time trends in MMS utilization. Although a few NMSCs in the Medicare population are treated with MMS, its utilization is increasing at a faster rate than the use of other treatment modalities, such as excision. The rate of Mohs surgery per 1000 Medicare beneficiaries increased by 236% between 1999 and 2009, whereas excisions and destructions of lesions increased by approximately 20%. It is unclear to what extent the increasing rate of Mohs surgery utilization is because of the epidemic increase in the incidence of NMSC over time, and to the increasing availability of Mohs surgeons, who were in short supply until 10 to 20 years ago. It has been suggested that previous lower utilization rates were associated with a lack of availability of Mohs surgery services. Mohs surgery was more likely than surgical excision on the face and less likely elsewhere. Tumor location was associated with MMS utilization, with 47% of facial lesions and 15% of lesions on the rest of the body treated with MMS. Patient age, race, and geographic region were also significantly associated with the likelihood of Mohs surgery. The use of Mohs for these cancers decreased with patient age (from 41% of patients aged 67 to 69 years to 34% of patients 85 years or older). Mohs was used in 37% of white patients, 23% of black patients, and 29% of patients of other races. Areas with high densities of Mohs surgeons were likely to have higher rates of MMS; however, some areas with low densities still had high rates of Mohs utilization. There was wide variation in regional MMS utilization and geographic disparity that warrants further investigation.

Use of curettage before Mohs

There is no standardized procedure for determining tumor margins before removing the first stage during MMS. Some Mohs surgeons perform light curettage of the tumor, which not only debulks the friable tumor tissue to facilitate tissue processing, but more importantly, can potentially help delineate its margins. Preoperative curettage has the potential to reduce the number of Mohs surgical stages required for tumor clearance, potentially increasing practice efficiency and decreasing cost of care. Several studies have examined the effectiveness of curettage in delineating tumor margins before MMS and have yielded different conclusions. Jih and colleagues studied 150 previously biopsied BCCs and SCCs less than 1.5 cm in size, dividing the study into 3 parts: (1) a retrospective study of 50 tumors curetted before MMS by a surgeon who routinely curettes preoperatively; (2) a prospective study in which a surgeon who routinely does not curette preoperatively curetted 50 tumors before MMS; and (3) a comparative historical group of 50 noncuretted tumors treated with Mohs surgery by the latter surgeon. Histologic evaluation of the curetted tissue revealed that only 50% had tumor in the curettings, but in 76% of these, the curette left residual tumor at the surgical margins. Of the remaining 50% in which the curette removed only noncancer–containing skin, 34% had tumor present at the surgical margin. Overall, the curette removed tumor, leaving no residual tumor at the surgical margins in only 12% of lesions. Comparison with historical noncuretted tumors operated on by the same surgeon showed that curettage did not affect the mean number of stages or the proportion of tumors requiring more than 1 stage for histologic clearance.

A prospective evaluation of 599 patients with biopsy-proven BCCs treated with MMS examined preoperative tumor size, curetted dimensions before the first surgical stage, proposed excisional margins before each surgical stage, and the final defect dimensions after each surgical stage were measured. Results showed that the curetted margin exceeded the observed extent of each tumor in most cases. A 1-mm excisional margin taken in the first stage of Mohs surgery without first performing curettage would have necessitated an extra surgical stage in 99.0% of the cases. These investigators concluded that careful presurgical curettage significantly reduces the number of Mohs surgical stages required for BCC treatment.

A recent study compared visual inspection, curettage, and dermoscopy in determining tumor extent before initial margins are taken for MMS. These investigators randomized 54 patients into 3 groups to delineate residual tumor (visual inspection, curettage, or dermoscopy) before MMS for BCCs on the nose and recorded the final number of stages and postoperative defect sizes. They found no statistically significant differences for the final number of stages ( P = .20) or the final defect sizes ( P = .47) among the 3 arms.

Part of the discrepancy between these studies lays in their design. In the study by Jih and colleagues, 100 of the 150 tumors studied were from the practice of 1 Mohs surgeon who, in all likelihood, did not value the use of curettage before MMS because he did not routinely use it in his practice. Results from a single surgeon, or a study in which 1 surgeon dominates the findings, may be prone to bias because of different value on the use of curettage and variation in technique (eg, differential application of pressure during curettage, number of passes). Also, in all studies, the outcome measures were not recorded by blinded observers, leading to the potential for further bias. To better answer this question, a study design is needed in which Mohs surgeons (balanced among those who favor and do not favor preoperative curettage) are randomized to curettage or none a priori, and rigorous blinded methodologies are used to measure outcomes. Until then, the value of preoperative curettage for MMS is still to be determined.

Use of prophylactic antibiotics

There is considerable practice variation in the use of prophylactic antibiotics for MMS. MMS is considered a clean surgical procedure (unless a tumor is secondarily colonized and infected), with an overall low rate of surgical site infection, estimated at around 0.7% to 2.5%. Similarly, the rate of bacteremia during dermatologic procedures is low, estimated around 1.9%. Yet prophylactic antibiotics may be administered to MMS patients despite a low risk of bacteremia and surgical site infections in most patients. There are some indications for prophylactic antibiotics that are clear (including history of immunosuppression [solid organ transplant recipient, human immunodeficiency virus with low CD4 count, chronic lymphocytic leukemia]). However, some Mohs surgeons routinely use prophylactic antibiotics for patients with a history of prostheses (valves or joints), nonphysiologic heart murmurs or valvular disease, or repair type (skin graft or large flap) in which the data are not supportive.

With regard to cardiac indications, the American Heart Association (AHA) released updated guidelines for antibiotic prophylaxis in 2007 that recommend their use to prevent bacteremia in dental, oral, upper respiratory tract, and some genitourinary and gastrointestinal procedures, in patients with high-risk or moderate-risk cardiac conditions. MMS does not usually fall into any of the categories outlined earlier, unless oral or respiratory mucosa is breached during the procedure. However, if MMS is planned on the lip or on the nose where breach of the nasal mucosa is anticipated, antibiotic prophylaxis is indicated for the following cardiac conditions:

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  Previous infective endocarditis

  
  
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  Prosthetic cardiac valves

  
  
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  Unrepaired cyanotic congenital heart defects, including palliative shunts and conduits

  
  
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  Congenital heart defects completely repaired with prosthetic material or a device, whether placed by surgery or by catheter intervention, during the first 6 months after the procedure

  
  
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  Repaired congenital defects with residual defects at the site or adjacent to the site of a prosthetic patch or prosthetic device

  
  
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  Cardiac transplants and development of cardiac valvulopathy.

Patient groups that may have received routine antibiotic prophylaxis in the past but are no longer candidates for it include those with mitral and aortic valve disease, rheumatic heart disease, or structural disorders like ventricular or atrial septal defects or hypertrophic cardiomyopathy, according to the AHA statement. Thus, prophylactic antibiotics are rarely necessary for patients who have cardiac disease undergoing MMS.

In general, systemic prophylactic antibiotics are not indicated in patients undergoing MMS who have vascular grafts, or orthopedic prostheses. However, there are certain instances when their use may be warranted. A recently published Advisory Statement for antibiotic prophylaxis in dermatologic surgery suggests their use in Mohs performed on the lower extremity/groin area in individuals with a total hip or knee replacement because of the documented increased risk of surgical site infection on the lower extremities. Mohs surgeons can use guidelines in formulating their approach based on individual patient characteristics and needs.

If antibiotic prophylaxis is deemed necessary, the most commonly used antibiotics for prophylaxis include dicloxacillin and cephalexin (2 g by mouth 1 hour before surgery). For patients who are allergic to penicillin, this author uses either cefdinir (600 mg by mouth 1 hour before surgery, unless the patient had an anaphylactic reaction to penicillin), azithromycin (500 mg by mouth 1 hour before surgery), or clindamycin (600 mg by mouth 1 hour before surgery). However, Mohs surgeons should strive to decrease unnecessary use of antimicrobials by avoiding them in situations in which good evidence indicates that they are ineffective.