Keys To Diagnosing Lower Extremity Melanomas

Given the possible dire consequences of melanoma, prompt diagnosis is vital. Accordingly, these authors review the current literature on imaging modalities, discuss appropriate staging and biopsy pearls, and offer a compelling case study.

   Evaluation of skin lesions is among the most common queries proposed by patients who present for both general and specialized medical care. While the exact management of such lesions is currently a topic of substantial controversy, the undisputable fact remains that certain diseases of the skin, including malignant melanoma, can and will result in death if they are inappropriately treated or go undiagnosed.

   Although the presentation of malignant melanoma may occur in any area of the body, up to one-third of all presentations occur in the foot or the distal lower extremity.1,2

   What is perhaps even more disturbing is that pedal distribution of melanoma is believed to be of a more advanced stage at the time of diagnosis due to its limited visibility, infrequent inspection and incorrect initial diagnoses.3

   In a clinical review of 38 melanoma patients, Gray and colleagues found that 32 percent of the melanomas in their series were initially diagnosed as benign lesions including bruises, granuloma, diabetic foot ulcers, warts or bacterial infections among others. They also found a significant difference in the thickness of lesions diagnosed at presentation (1.74 mm) versus late diagnosis (5.8 mm).3

   The primary approach recommended for assessment of pigmented lesions suspicious for melanoma is the ABCD qualification that Friedman described in 1985.4 One would evaluate a lesion for asymmetry, border, color and diameter. Full thickness dermal biopsy with histopathological examination is considered the standard of care for any lesion that raises a high index of suspicion for melanoma based on the above criteria.5,6

Assessing The Strengths And Drawbacks Of Dermatoscopy

   Given the poor prognosis associated with delayed presentation and intervention, more aggressive surveillance is critical to improve outcomes. Aside from inquisitive visual detection, adjunctive diagnostic imaging to help facilitate diagnosis includes dermatoscopy, laser microscopy, optical tomography and high-resolution ultrasound.7

   Perhaps the most promising of the imaging techniques is dermatoscopy (also known as dermoscopy or epiluminescence microscopy).7 The primary goal of dermatoscopic examination is to differentiate between benign and malignant lesions. The technique involves the use of an oil-to-skin interface under magnification, which allows greater visualization of the epidermis and superficial dermis.7,8 While this method is not diagnostic in and of itself, it can be useful to help increase or decrease confidence that a lesion is benign or malignant based on features one visualizes during examination.7

   For example, during the evaluation of non-melanotic lesions, findings such as milia-like cysts represent seborrheic keratosis and a white scar-like patch may represent dermatofibroma. In addition, a homogeneous blue color will represent a blue nevus, red-black-blue lacunae represent angioma and arborizing vessels with blue-grey globules represent basal cell carcinoma.7

   However, dermatoscopic examination is highly user-dependent and results are variable in inexperienced hands.6-8 A meta-analysis of studies evaluating dermatoscopy found that this diagnostic technique was more accurate than clinical examination alone. However, the researchers noted that many of the lesions identified as negative by dermatoscopy went on to biopsy nevertheless, negating the clinical significance of the technique.8

   The role of dermatoscopy may be more beneficial when there is greater morbidity associated with biopsy. Examples may include lesions on the face or hands, and perhaps patients with several questionable lesions. Goodsen describes the “ugly duckling sign” in which one compares multiple lesions and identifies any that are unique relative to its neighbors.7 One would use the dermatoscope to evaluate the signature nevi or consistent appearing lesions while physicians should always biopsy the aberrant lesion.

What You Should Know About Tumor Biopsies And Classifications

   While clinically helpful, no current visual imaging techniques can substitute for full thickness dermal biopsy with histopathological examination, particularly given the potentially devastating consequences associated with an inaccurate diagnosis.

   When the clinician is suspicious of melanoma, a full thickness incisional or excisional dermal biopsy is crucial in order to guide further management. One should never use a shave biopsy to evaluate a suspicious lesion as tumor depth is the most important factor in determining treatment.

   Once you have obtained a biopsy, the depth of the lesion will determine the marginal excision, provide guidance for node dissection and assist in predicting the mortality rate.5,6 During excisional biopsy, narrow margins of 2 to 3 mm are advised to preserve lymphatic flow, which will improve the accuracy of sentinel lymph node mapping.6

   When a biopsy returns positive for melanoma, the anatomic level of invasion (Clark’s level) and the maximum depth or thickness (Breslow’s depth) help determine the course of action.5,9 Research has recently shown that Clark’s levels are only prognostic for tumors less than 1 mm thick.10

   In order to facilitate a more accurate staging arrangement, the American Joint Committee on Cancer (AJCC) developed the Tumor-Node-Metastasis (TNM) classification for melanoma. This classification incorporates thickness, ulceration, lymph node metastasis, regional metastasis and distant metastasis.

   Depth of the lesion determines the appropriate margins for wide excision. Melanoma currently has no pharmacologic cure once it has metastasized to visceral organs, thus leaving primary resection prior to metastasis as the foundation for intervention.

What Is The Prevailing Thinking On Resection Margins?

   In 2004, Tsao and co-workers reviewed several randomized controlled trials that have identified the recommended resection margins based on tumor thickness.5 A resection margin of 0.5 to 1.0 cm is considered adequate for melanoma in situ. As far as lesions with depth identified at <1 mm, one should excise them with a 1.0 cm margin. Tumors with a depth of 1.01 to 2.0 mm should undergo excision with margins of 1.0 to 2.0 cm. Any tumor with a depth greater than 2.01 mm should have a resection margin of at least 2.0 cm.9

   Currently, there remains some controversy regarding the size of resection margins with some authors recommending narrower margins as recent prospective trials have reported equivocal results for wider versus narrower margins.11 Clearly it would be both advantageous and favorable to the patient to have a more narrow yet safe margin for resection. This is particularly true in high-risk areas such as the ankle or foot in which large radical resections can pose great morbidity and challenge closure of the surgical wound.

   The advantage of a 2 cm resection in comparison with a 5 cm margin is a reduction of approximately 50 percent of post-excision wound width depending on size of the lesion. Smaller margins could reduce the need for skin grafts, flaps and potentially even amputation.

Pertinent Insights On Sentinel Lymph Node Biopsy

   In order to provide the most precise prognosis once one has identified melanoma, sentinel lymph node (SLN) biopsy has been widely encouraged. Many consider SLN to be the standard of care for certain melanomas.12

   The International Sentinel Node Society (ISNS) recently released a consensus statement on SLN biopsy for melanoma, recommending that one offer SLN biopsy to all patients with melanoma depth greater than 1.0 mm.12 The panel also agreed that SLN biopsy should be the standard of care for staging melanoma based on the incorporation of nodal metastasis in the AJCC TNM classification scheme.

   In 1999, Haddad and co-authors identified a positively proportional relationship between tumor thickness and nodal involvement. They note that depths of <0.76 mm, 0.76 to 1.0 mm, 1.0 to 1.5 mm, 1.5 to 4.0 mm, and > 4.0 mm have respective rates of lymph node involvement of 0 percent, 5.3 percent, 8 percent, 19 percent and 29 percent.13

   One can evaluate lymph nodes by elective node dissection (ELND), sentinel lymph node biopsy (SLNB) or open lymphadenectomy.14 Morbidity associated with open lymphadenectomy can be severe with greater development of lymphedema. This result often decreases with SLN biopsy procedures.

   The AJCC recommends histopathological evaluation of nodes for classification schemes greater than TNM Stage II, with SLN biopsy commonly recommended prior to consideration of total lymphadenectomy.15,16 When it comes to a SLN biopsy, the physician would inject radioactive or vital blue dye around the skin lesion within the lymphatic basin prior to the procedure. Then he or she would use a gamma probe intraoperatively to identify “hot” nodes for resection.

Case Study: When A Recurring Ulcer Is Diagnosed As Melanoma

   A 46-year-old Caucasian male had a consultation for evaluation of a chronically ulcerated lesion on the plantar aspect of his left foot. He had no pertinent medical history and did not have a familial history of melanoma or any malignancy.

   The patient related a history of trauma to this area. Four years prior to presentation, he suffered a puncture laceration from a wooden foreign body into the area of the current ulcer while he was walking barefoot. Following the initial injury, the wound had closed uneventfully. Within weeks of the original injury, the patient observed that the area had re-ulcerated despite complete initial closure of the laceration.

   The patient went to his primary care physician, who advised him to continue with local wound care including a topical antimicrobial ointment and simple dressings. He returned to his primary care provider 10 months later with a notable increase in the size of the lesion. This prompted referral to our hospital-based wound clinic.

   Upon inspection, the lesion measured approximately 4.5 cm x 1.5 cm and had a longitudinal orientation between the second and third metatarsal heads. The lesion was ulcerated with a hypergranular base. There was an asymmetrical margin and dark discoloration within and surrounding the lesion. There was sharp demarcation with no corresponding erythema or evidence for infection. The physician obtained magnetic resonance imaging (MRI) to evaluate for depth and to confirm or exclude communication with deeper structures. The imaging identified that this was a localized soft tissue mass without abscess or underlying osseous involvement.

   The physician performed an excisional biopsy with narrow margins to facilitate primary closure. The excised mass measured 6.0 cm x 3.0 cm. The physician sent the specimen for histopathological evaluation and it was identified as a superficial spreading melanoma in the vertical growth phase. The specimen had a Breslow’s depth of 5 mm and was identified as a Clark’s level V lesion. The margins of the distal lateral mass were positive for melanoma involvement as well as the deep margin at the center of the specimen. The other remaining margins were negative.

The biopsy reports includes the AJCC staging:

   • TNM: pT4bNxMx
   • AJCC: at least Stage pIIC (0-IV)

   The code pT4b indicates that the tumor is greater than 4 mm thick (T4) and “b” denotes ulceration.17 No nodes or metastases have been evaluated yet and thus are noted with the “x.” The AJCC staging equals Stage II or greater depending on nodal involvement (see “A Guide To Staging For Melanoma” at the left).17

   The patient received a referral to a general surgeon, who advised a wide local excision and sentinel node biopsy of the inguinal lymph nodes. Since wide excision would preclude primary closure, a plastic surgeon also consulted for a free flap. Excision of the previous surgical scar occurred with greater than 2.5 cm margins. The wide local excision procedure included the subcutaneous tissue plane as well as the plantar fascia. The sentinel lymph node biopsy was positive in three out of three specimens.

The AJCC staging was revised to:

   • TNM: pT4bN2aMx
   • AJCC- TNM: pIIIC

   Again, the tumor is T4b from the initial biopsy. There were three positive nodes, which mandates a Stage IIIC and metastases are not yet evaluated.

   Following the positive SLN biopsies, the patient underwent a complete open lymphadenectomy of the deep and superficial inguinal nodes. This identified one of 13 nodes to be positive. A total of four out of 16 nodes were involved.

   A position emission tomography (PET) scan demonstrated focal uptake in the pectoralis minor muscle belly. General surgeons performed complete deep inguinal node dissection and interventional radiology assessed the pectoralis muscle biopsy. A total of four of 16 nodes were positive and the muscle biopsy was negative. They identified no metastases outside of the lymphatic system.

   The flap is healthy and viable after minor early superficial dehiscence. The patient is tolerating a return to weightbearing. The final AJCC staging in this case is:

   • TNM: pT4bN2aM0.

In Conclusion

   The diagnosis of melanotic tumors within podiatry office settings likely arises from one of two situations. The lesion is either a chief complaint of the patient or the lesion is completely an incidental finding during the standard examination completed by the physician.

   In the situation in which the patient presents with a chief complaint of a pigmented lesion, the physician could perhaps infer a more advanced lesion based on the observation that many patients will have waited for a remarkable occurrence such as an ulceration or significant change in characteristics prior to presentation.

   Patients will often rely upon podiatric physicians to be the “authority” to provide an accurate diagnosis in situations such as with skin tumors and lesions of the lower extremity. Quite often, these individuals presenting to the office will have already been “observed” by providers within a primary care setting for months, if not years, prior to presentation. This makes your consultation even more crucial to the patient’s well being.

   Once the patient presents, there is no place for further “observation” of any lesion considered to be suspicious for melanoma. Action is required. Accordingly, obtaining a full thickness dermal biopsy with histopathological evaluation is a critical component to the evaluation and management of these patients. As surgical subspecialists, podiatric physicians have a responsibility to offer and recommend biopsy in these circumstances.

   The case presentation illustrates the role of podiatric physicians in diagnosing suspicious lesions by performing an excisional biopsy with urgency upon the patient’s presentation to the clinic. This situation also demonstrates the collaboration or “team approach” that is required among other medical specialties in order to diagnose and manage patients with melanoma successfully.

Dr. Moen is a second-year podiatric medical and surgical resident at the Mercy Hospital PM&S-36 Residency program in Coon Rapids, Minn.

Dr. Zelent is a staff podiatrist for the North Memorial Medical Center in Robbinsdale, Minn., and has a faculty appointment with the Mercy Hospital Podiatric Medical and Surgical Residency Program (PM&S-36) in Coon Rapids, Minn.

For further reading, see “What You Should Know About Malignant Melanoma” in the April 2008 issue of Podiatry Today, “Expert Insights On Diagnosing Pigmented Skin Lesions” in the April 2005 issue or “Identifying Skin Malignancies On The Distal Lower Extremity” in the September 2003 issue.

To access the archives or get reprint information, visit www.podiatrytoday.com.

References:

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