Introduction

Recent literature has established that there is much for the medical community to learn about highly pigmented skin, specifically in the realm of wound healing and even more so in diabetic foot ulcers (DFUs). Most distressing is the higher prevalence of amputation and mortality among patients with skin of color and DFUs as opposed to their Caucasian cohorts. In fact, a 2022 study found that patients identifying as Black were approximately 4% more likely to experience above-ankle amputation or death.¹

Identifying Physiological Characteristics of Skin of Color

To begin, clinicians can look to available general dermatological information and the science of skin pigmentation. Highly pigmented skin has different properties with respect to structure and function and, therefore, may exhibit differences in wound healing. Various skin-related conditions, including DFUs, may appear significantly different between varying skin tones.²

Melanin is a key determinant of skin pigmentation.² Melanocytes produce melanin in the basal epidermal layer of the skin. Melanosomes then transport the melanin into keratinocytes. Several factors then influence skin pigmentation, such as the size and distribution of melanosomes, timing of melanin degradation, and type of melanin.²

Clinical Challenges Related to DFUs in Highly Pigmented Skin

Erythema, often presenting as redness, is one key factor evaluated in DFUs that can be challenging to detect in pigmented skin. The redness visible against lighter skin tones that often alerts clinicians to inflammation or infection is usually not present in skin of color or may be somewhat masked.² Associated inflammatory changes may also appear differently, as more brown, grey, purple, or black. The appearance of pressure injury or shear forces can also be difficult to discern in skin with darker pigmentation, contributing to delays in recognition of preulcerative states by both patients and clinicians.³

Unique changes in skin texture or contour may pose challenges to diagnosis. Clinicians will also note that skin of color may be thicker (by micrometers) and appear drier than skin with lighter pigmentation.^4,5 These states are due to additional corneocyte layers and a higher risk for transepidermal water loss and xerosis, respectively, which are essential to keep in mind when assessing risk for skin breakdown like DFU and during treatment.

Overall, changes in coloration and texture, as described above, can make it more difficult to identify related conditions such as ischemia, lymphangitis, and infection in DFUs,⁶ so it behooves health care professionals to be familiar with these differences in order to maintain the most accurate clinical index of suspicion.

Post-Inflammatory Response in Skin of Color

The post-inflammatory process is another instance where melanin plays a role in wound healing. Post-inflammatory hyperpigmentation or hypopigmentation may arise due to trauma, inflammation, or other skin damage, such as from a DFU.² Hyperpigmentation triggers increased melanin production, which is deposited in the surrounding epidermal keratinocytes. Occasionally, this melanin will be found in the deeper dermal layer. Hypopigmentation, although less common than hyperpigmentation, can also occur from similar stimuli, which results in decreased melanin production or a loss of melanocytes.² Either presentation has the potential to confound continued assessment during treatment. For example, one should be cautious to avoid misdiagnosing hyperpigmentation as eschar or necrosis or vice versa.⁶

Additional Educational and Logistical Challenges to Consider

Unfortunately, there is a gap in available education and evidence on DFU management in patients with diverse skin types. This gap is evident in the available classification systems that help describe skin types and pigmentation. Dermatologic practice most frequently uses the Fitzpatrick Skin Phototype, but this scale is not typically applied to assessment and documentation of DFUs. Alternate classifications also exist but also suffer the same challenges to DFU applicability.² Although not specific to DFUs, but at least directed at wound care, the 2019 National Pressure Injury Advisory Panel guidelines discuss using a color chart such as the Munsell skin tone chart to describe and classify observation of various skin tones objectively.⁴

Key Obstacles Related to Differential Diagnosis

There is a particular complexity noted in the literature regarding DFUs in general and the potential misdiagnosis of skin cancers. Although this is not yet directly tied to skin of color, there is a logical association to consider. Dermal malignancies can clinically mimic DFUs, including melanoma, squamous cell carcinoma, certain lymphomas, and Kaposi’s sarcoma, and may have ulcerative properties.⁷ Such mimicry is more prevalent in patients over age 65.⁷

However, as previously stated, there is a scarcity of literature surrounding DFU in highly pigmented skin. There are discussions of a lack of lower extremity-related publications on the diagnosis of melanoma in patients with Fitzpatrick skin types 5 or 6.⁸ Therefore, given the challenges in visual assessment of DFU-appearing presentations in those with pigmented skin, dermatologic malignancies should be part of an overall differential diagnosis, and biopsy may be a vital tool in these cases.

Important Considerations During and After DFU Healing

When wounds like DFUs heal, scar formation is expected. Collagen and extracellular matrix (ECM) are produced by fibroblasts when scar tissue is formed.⁹ However, in patients with diabetes, this process is different, and scars have lower collagen synthesis and exhibit a different overall structure, with lower tensile strength, increased collagen density, and reduced contractibility. They rely more on the processes of re-epithelialization and granulation than on contraction, which can make diabetic scars more susceptible to trauma like tension and shear forces.⁹

These challenges may magnify, though, for patients with skin of color. Increased inflammation in DFUs can lead to a higher risk for hypertrophic or keloidal scarring.⁹ Keloids are benign but potentially hyperproliferative scars that impact 4.5-16% of the Black and Hispanic populations in the United States.² When keloids form, it is possible for the scar tissue to continue to worsen over time and to extend beyond the original wound borders. This process is thought to possibly result from reduced levels of collagenase, an enzyme that breaks down collagen. Family history of keloidal scarring is present in 5-10% of those that form them and is thought to be, in part, hereditary.²

Connecting these sets of information, increased collagen density in patients with diabetes and decreased collagen breakdown in patients with skin of color could lead to an amplified risk of such abnormal scarring. Depending on the size, location, and characteristics of these hypertrophic or keloidal scars, they may pose a risk for subsequent skin breakdown and DFU recurrence.

DFU Assessment Pearls for Highly Pigmented Skin

As with all wound assessments, a thorough history is important in this patient population. Specifically, it is vital to elucidate any history of pressure, friction, or other macro- or microtrauma to the foot in patients presenting with a DFU, and even more so in patients with skin of color since visual signs of such injuries will not always be clear.⁴

To enhance the accuracy of visual inspection, one may choose natural or enhanced lighting when possible. It is essential to know that fluorescent lighting may cast blue tones on darker skin.⁴ It is also wise, when possible, to use skin in a comparable alternate location as a comparison to assess for contrast in appearance. For DFUs, this may be the contralateral foot or limb in a comparable location (dorsal versus plantar foot), but remember that this may not always be possible in cases of amputation.⁶

Palpation also becomes an important tool, specifically to assess for signs of temperature changes or fluctuance of tissues that may alert the clinician to infection or other important states.

Technology may also serve as an adjunctive tool when visual assessment alone is problematic. Options like infrared thermography or subepidermal moisture readings may hold value for clinicians.⁴ One recent presentation looked at bacterial load via fluorescence imaging.¹⁰ They found a 12-times increase in detection sensitivity across all skin tones compared to standard assessment for at-risk and clinically infected wounds, which increased further when the clinician analyzing the information was an expert in the technique.¹⁰

What Will The Future Bring?

The hope is that there will be continued generation of research and high-quality literature on diabetic foot ulcers in highly pigmented skin, including honing expertise in assessment, diagnosis, and optimizing treatment. Additionally, clinicians may continue to learn more about the role of technology in achieving these goals. There are early discussions of what part machine learning may be able to play, including in classifying infection, ischemia, malignant transformation, and other metrics.¹¹

Appropriate and comprehensive assessment and care for wounds in patients with skin of color is vital, as one study found that Black patients were nearly twice as likely to undergo a lower limb amputation within a year of DFU diagnosis compared with Caucasian/Non-Hispanic patients.¹² Another study identified significantly higher risks of major amputation for African-American, Hispanic, and Native-American patients with diabetic foot infections.¹³ Overall, however, enhanced awareness of the need for careful and thoughtful assessment methodology, along with a desire to learn how to best care for all unique patient populations, will likely serve wound care clinicians well.

References

1. Brennan MB, Powell WR, Kaiksow F, et al. Association of Race, Ethnicity, and Rurality With Major Leg Amputation or Death Among Medicare Beneficiaries Hospitalized With Diabetic Foot Ulcers. JAMA Netw Open. 2022;5(4):e228399. doi:10.1001/jamanetworkopen.2022.8399
2. Hutchison E, Yoseph R, Wainman H. Skin of colour: essentials for the non-dermatologist. Clin Med J. 2023;23(1):2-8.
3. Harms S, Bliss DZ, Garrard J, Cunanan K, Savik K, Gurvich O, Mueller C, Wyman JF, Eberly L., Virnig B. Prevalence of pressure ulcers by race and ethnicity for older adults admitted to nursing homes. J Gerontol Nurs. 2014, 40, 20–26.
4. Black J, Simende A. Ten top tips: assessing darkly pigmented skin. Wounds Int. 2020;11(3):8-11.
5. Evoria AS, Adams MJ, Johnson SA, Zhang Z. Corneocytes: Relationship between structural and biomechanics properties. Skin Pharmacy Physiol. 2021;34:146-161. https://doi.org/10.1159/000513054
6. Dhoonmoon L, Fletcher J, Atkin L, et al. Addressing skin tone bias in wound care: assessing signs and symptoms in people with dark skin tones. Wounds UK. 2021; Available at: https://www.wounds-uk.com/resources/details/addressing-skin-tone-bias-w…. Accessed March 14, 2023.
7. Lyundup AV, Balyasin MV, Maksimova NV, et al. Misdiagnosis of diabetic foot ulcer in patients with undiagnosed skin malignancies. Int Wound J. 2022;19(4):871-877.
8. Jicman PA, Smart H, Ayello EA, Sibbald RG. Early malignant melanoma detection, especially in persons with pigmented skin. Adv Skin Wound Care. 2023;36(2):69-77.
9. Dasari N, Jiang A, Skochdopole A, et al. Updates in diabetic wound healing, inflammation, and scarring. Semin Plast Surg. 2021;35(3):153-158.
10. Johnson J, Johnson Jr A, Andersen C, Kelso MR, Oropallo A, Serena TE. Closing the gap on racial disparities in diagnosis of chronic wound infections: the concerning trend involving skin pigmentation and a role for fluorescence imaging. Presented at the Symposium on Advanced Wound Care Fall. October 2022. Las Vegas, NV.
11. Ahsan M, Naz S, Ahmad R, Ehsan H, Sikandar A. A deep learning approach for diabetic foot ulcer classification and recognition. MDPI. 2023;14(1):36.
12. Miller TA, Campbell JH, Bloom N, Wurdeman SR. Racial Disparities in Health Care With Timing to Amputation Following Diabetic Foot Ulcer. Diabetes Care. 2022;45(10):2336-2341. https://doi.org/10.2337/dc21-2693
13. Tan TW, Shih CD, Concha-Moore KC, Diri MM, Hu B, Marrero D, Zhou W, Armstrong DG. Disparities in outcomes of patients admitted with diabetic foot infections. PLOS ONE. 2019;14(4):e0215532. https://doi.org/10.1371/journal.pone.0215532