Case report of melanoma misdiagnosed as diabetic foot ulcer
Malignant melanoma is a fatal form of skin cancer. There are several treatment options for treating malignant melanoma. Surgery is preferred in the early stages and can be curative on its own. Patient education is an essential part of the preventive and therapeutic strategy, as many cases of malignant melanoma are discovered by the patients themselves. Treatment failure or late diagnosis can have unfortunate consequences. Diabetic foot ulcers (DFUs) are a common, but serious, complication of diabetes with a global prevalence of 6.3%1 and a lifetime incidence of 25%.2 Very often, patients fail to tell their doctor about new lesions on their feet. Therefore, it is important that doctors do a thorough examination of the feet each time patients present in order to more easily detect these lesions. About 85% of non-traumatic lower limb amputations occur in patients with diabetes.3 The differential diagnosis of DFU is broad and includes malignant tumors (squamous cell carcinoma, basal cell carcinoma, Kaposi’s sarcoma, malignant melanoma, Merkel cell carcinoma, Mycosis fungoides), infections (deep and superficial cutaneous mycosis, mycobacterial infections), Lipoid necrobiosis, bedsores, vasculopathies (warfarin-induced necrosis, factor V Leiden deficiency, cholesterol embolism, calciphylaxis), pyoderma gangrenosum, venous ulcers, hypertensive ulcers (Martorell).4 Diabetes itself increases the risk of skin cancer.5 This increased risk is not only due to the diabetes itself, which can generate a locus minoris resistentiae,6 that is, an underlying tendency to cancer, as seen in other immunodeficiency states,6 but this increased risk of skin cancer may be associated with drugs often used to treat the common comorbidities of diabetes, such as hydrochlorothiazide.7.8 Part of the risk of the latter drug may be related to its potential phototoxicity.8 Without the input of a multidisciplinary specialist, who can help differentiate malignant ulcers from benign ulcers, often by detecting subtle signs, these malignant ulcers can go undetected for long periods of time.9 Such cases are denied prompt and adequate treatment due to misdiagnosis or late diagnosis.
Presentation of the case
A 75-year-old Caucasian male with long-standing type 2 diabetes presented with a 2-3 year history of painless right heel ulcer. The ulcer had gradually enlarged, despite adequate treatment. He had received various therapies for a diagnosis of diabetic foot ulcer, without experiencing significant improvement. Physical examination showed an ulcerated, fungal, black plaque covering his right heel, with a white fissure extending 12 hours to the middle of the lesion (Figure 1). There was minimal bleeding. No inguinal lymphadenopathy was palpated.
Figure 1 Melanoma of the right heel. Straight heel, with a well-defined black plate. There are signs of bleeding and a white fissure extends for 12 hours in the center of the lesion.
A biopsy was performed, which revealed a BRAF-negative malignant melanoma, with a vertical growth phase, Breslow 3.1 mm, ulceration, 11 mitoses / mm,2 Clark level IV, no lymphatic or vascular invasion observed. Sampling of the right inguinal lymph nodes did not suggest any involvement, but PET scans showed involvement of the lung, right inguinal lymph nodes, and bone. A schedule detailing the various tests performed can be found in Table 1.
Table 1 Schedule of tests carried out
The patient was referred to oncologists.
Acral lentiginous melanoma or acral melanoma was first described in 1977 by Arrington et al.ten It is the least common form of melanoma, accounting for 1 to 2% of cases11 and has a lower survival rate than other forms of melanoma.11 Therefore, prompt diagnosis of this form of melanoma is essential for patient survival.
Acral lentiginous melanoma is often found on areas of the foot subject to pressure and trauma, such as the heel, lateral aspect of the foot, and forefoot,ten which are also areas where DFU is commonly present. Confusion, leading to a wrong diagnosis, can lead to a delayed diagnosis and therefore a poorer prognosis, as in this case. Our case presented with a multi-year heel ulcer which, due to its location and the patient’s underlying diabetes, was diagnosed and managed as a diabetic foot ulcer. Acral melanoma has also been misdiagnosed as interdigital tinea pedis,12 illustrating the immensity of differential DFU diagnoses.4.9.12 Failure to heal with worsening ulcer, despite treatment, did not appear to trigger an earlier reassessment for skin malignancy or other differentials, possibly because DFUs are notoriously difficult to heal. This difficulty in healing may be the reason why, even in a self-treating physician, melanoma was misdiagnosed and treated as a DFU.13
A referral for specialist care (dermatology) might have discovered subtle signs that were easily missed at the primary care level. In many centers around the world wound care is often not performed by dermatologists, but by primary care staff, so such cases can “slip through the cracks”. Our study is limited by the fact that it is a case study and not a large review; however, the case itself illustrates why differential diagnoses of DFU should always be considered in each patient and multidisciplinary teams are needed for adequate management of DFU.
DFUs are a common but serious complication of diabetes. As a result, the default diagnosis for foot ulcers in patients with diabetes is often diabetic foot ulcer. Staff who regularly care for patients with foot ulcers should be aware of other differential diagnoses of DFU, including malignancy, and should be prepared to promptly refer ulcers that do not respond to adequate care. There is also a need for dermatologists to be more involved in DFU care, as they are uniquely positioned to recognize the subtle telltale signs that could indicate a diagnosis like this. In such cases, failure to reach a prompt and accurate diagnosis could prevent the patient from receiving prompt and adequate treatment.
Ethics and consent
Written informed consent for the publication of this case was provided by the patient for the publication of the photographs and all test results.
Institutional approval was not required as this is a case report and the patient had previously given written informed consent for the publication of photographs and all test results.
The current work has been academically supported by the University ‘Dunarea de Jos’ of Galati, Romania, through the research center – Integrated Multidisciplinary Center for Research on Dermatological Interfaces (MIC-DIR).
This work was supported by the “Dunarea de Jos” University of Galati, Romania.
The authors report no conflicts of interest in this work.
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