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 Table of Contents  
Year : 2023  |  Volume : 19  |  Issue : 1  |  Page : 70-72

Annular pigmented actinic keratosis mimicking lentigo maligna melanoma in a 75-year-old female: An unusual presentation

Department of Dermatology, KJ Somaiya Medical College, Mumbai, Maharashtra, India

Date of Submission09-Jan-2023
Date of Decision23-Jan-2023
Date of Acceptance30-Jan-2023
Date of Web Publication17-Mar-2023

Correspondence Address:
Hari Pathave
Department of Dermatology, KJ Somaiya Medical College, Mumbai, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jiag.jiag_1_23

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Pigmented actinic keratosis (PAK) is an uncommon variant of actinic keratosis that can mimic different pigmented lesions, which may be benign or malignant. The diagnosis of PAK is often challenging because of overlapping features with lentigo maligna melanoma (LMM). Clinically, lesions of both conditions almost look similar; the diagnoses must be established histologically and with the help of immunostaining whenever needed. The distinction between a large PAK and LMM is important because their prognosis and management differ. We present a 75-year-old female with annular brown-to-black-colored maculo-plaque on forehead having clinical suspicious of melanocytic malignancy; which was diagnosed with a PAK on biopsy with help of histopathology and confirmed with Melan A/MART-1 immunostaining.

Keywords: Lentigo maligna melanoma, Melan A/MART-1, pigmented actinic keratosis

How to cite this article:
Pathave H. Annular pigmented actinic keratosis mimicking lentigo maligna melanoma in a 75-year-old female: An unusual presentation. J Indian Acad Geriatr 2023;19:70-2

How to cite this URL:
Pathave H. Annular pigmented actinic keratosis mimicking lentigo maligna melanoma in a 75-year-old female: An unusual presentation. J Indian Acad Geriatr [serial online] 2023 [cited 2023 Mar 22];19:70-2. Available from: http://www.jiag.com/text.asp?2023/19/1/70/371894

  Introduction Top

Actinic keratosis (AK) is considered to be an in situ epidermal dysplasia.[1] It may be erythematous or pigmented; pigmented AK (PAK) is significant also because of the variety of conditions both benign and malignant that it can simulate.[2] Of particular import, it can be confused with lentigo maligna melanoma (LMM) both clinically and histopathologically. The clinical resemblance arises as they are located primarily on sun-exposed areas such as the face, are sized greater than 1.5 cm, display various degrees of brown-gray-black pigmentation, and demonstrate variation in consistency that spreads radially.[3] The histopathologic difficulty in distinguishing PAK and melanoma in situ (LMM) occurs when it is not clear whether the pigmented atypical cells in the basal layer are keratinocytes or melanocytes.[4],[5] In such cases, immunostaining by Melan A/MART-1 is very helpful for the confirmation of diagnosis. This has obvious implications as the two conditions have very different prognoses and levels of concern with LMM requiring total excision with histologic assessment and PAK only requiring mild destructive therapy such as cryosurgery.[5] We are notifying a case of PAK in a 75-year-old female presented with annular maculo-plaque on the forehead, with size of 7 mc × 6 cm and brown to black pigmentation, clinically mimicking LMM which was diagnosed on histopathology and confirmed with Melan A/MART-1 immunostaining.

  Case Report Top

A 75-year-old female presented with dark-colored raised lesion on the right side of the forehead. The lesion started small flat brown discoloration 1 year back which gradually increased in size and shape radially to the present size without any itching, burning, or pain. There was not prior history of any drug intake, tattooing, or bleeding. She was a farmer by occupation and had frequent sun exposure since last many years. She did not have any systemic complaint. Cutaneous examination revealed single annular brownish-to-black-colored maculo-plaque of sized 7 cm × 6 cm on the right side of the forehead [Figure 1]. As there were color variations, variations in consistency (maculo-plaque), and size of >1.5 cm, we considered provisional diagnosis of LMM and differential diagnosis of pigmented basal cell carcinoma. The routine laboratory investigations were within the normal limits.
Figure 1: Annular maculo-plaque of 7 cm × 6 cm with gray to black pigmentation without surface change on right side of forehead and eyebrow

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We took biopsy from the lesion which showed mild focal epidermal hyperplasia with disorderly arrangement of keratinocytes and mild cytological atypia in the lower epidermis with increased basal pigmentation [Figure 2] and [Figure 3]. The stratum corneum was orthokeratotic with focal parakeratosis. There was sparing of adnexal epithelium. The dermis showed a moderately dense patchy lichenoid lymphocytic infiltrate and multiple melanophages with solar elastosis. On the basis of these findings, we diagnosed case as PAK and confirmed with Melan A/MART-1 immunostain which showed focal increased number of melanocytes in basal layer without cluster formation and no pagetoid upward migration of Melan A positively staining cells [Figure 4]. There were not Melan A staining cells in follicular epithelium and dermis.
Figure 2: (a) Biopsy shows focal epidermal hyperplasia with focal parakeratosis and superficial perivascular infiltrate (H and E, ×4) (b) Upper and mid dermal solar elastosis with melanophages and epidermal changes sparing adnexal epithelium (H and E, ×10)

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Figure 3: (a and b) Disorderly arranged keratinocytes and mild cytological atypia in lower epidermis with increased basal pigmentation (H and E, ×40)

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Figure 4: (a and d) Increased basal layer Melan A staining with sparing of follicular epithelium (Melan A/MART-1 immunostain, ×10) (b and c) Focal increased melanocyte number with increased staining in basal layer without clusters or pagetoid upward migration of cells and also without dermal melanocytes (Melan A/MART-1 immunostain, ×40).

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We started her on topical fluorouracil 1% cream (once daily) and imiquimod 5% cream (alternate day) with daytime sunscreen lotion. As patient refused cryotherapy, we continued medical treatment. After 1 month of treatment, there was improvement in form of flattening of plaque component and color became slight faint. We continued same treatment and advised strict sunprotection but unfortunately she lost to follow-up after 1 month.

  Discussion Top

PAK was initially described by James et al. in 1978,[6] and subsequently by Subrt et al. in 1983.[7] They noticed spreading lesions having similar variation in texture and size in four patients.

A several theories are proposed for its etiology. The Dinehart and Sanchez study demonstrated increased melanosome in keratinocytes.[8] The color of lesion is due to an excessive melanin in keratinocytes and melanophages.[7],[8] The more number of dermal melanophages may indicates melanosomes with abnormal degranulation.[8]

Majority actinic keratoses usually appear as an erythematous plaque, but rare variant present as a pigmented lesion. PAK commonly presents as brown-to-black-colored papules or plaques on sun-exposed areas of size ranging from <1 cm to more than 5 cm in diameter.[9] Most PAK presents as progressive growth, as “spreading” or “centrifugal.”[10] Our case had similar annular pigmented maculo-plaque of more than 5 cm and with variation in colors, so we suspected LMM.

Skin punch biopsy is necessary to differentiate PAK from LMM since they share many dermoscopic features. The dermoscopic features of a PAK contain a pseudo network and gray or black dots and globules.[11] However, features such as pseudo networks and hyperpigmented globules are also present in LMM; therefore, histopathology is the gold standard for establishing a diagnosis.[12]

The histopathology of non-PAK shows solar elastosis in the dermis with cytologic atypia of the basal keratinocytes and parakeratosis in which there is sparing of the follicular epithelium. In addition to the features observed in non-PAK, PAK will also show increased melanin within the epidermis and dermis.[11] Biopsy in our case showed similar findings to consider the diagnosis of PAK.

On clinicopathology correlation, it was almost clear about the diagnosis of PAK but as there were a greater number of vacuolated cells in lower epidermis, we performed Melan A/MART-1 immunostaining for confirmation, which showed focal increased number of Melan A staining cells with dendrites in basal layer without clusters or pagetoid upward migration. Hence, it was noted that along with increased melanin in epidermis and dermis, melanocyte number was also increased in PAK.

Treatment options for PAK are the same as that for non-PAK. Lesions may be treated using cryotherapy with liquid nitrogen. Topical therapy with either 5-fluorouracil, imiquimod, or ingenol, curettage, photodynamic therapy, and superficial peels may be used when there are multiple lesions.[13] In our patient, we treated PAK with topical 5 fluorouracil and imiquimod cream as patient was refused cryotherapy treatment. After 1 month of treatment, there was improvement in the lesion in form of flattened plaque area and color became faint and she is now on regular follow-up.

  Conclusion Top

Annular PAK can present as maculo-plaque with variation in colors and of size more than 5 cm on sun-exposed area mostly in aged person which can mimics LMM and as dermoscopic features of both may be similar; dermatopathology is a gold standard for diagnosis and Melan A/MART-1 immunostaining can be used for further confirmation. Hence, treating dermatologist should be aware and cautious about both conditions as lentigo maligna needs more aggressive and destructive treatment.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Ciudad C, Avilés JA, Suárez R, Lázaro P. Diagnostic utility of dermoscopy in pigmented actinic keratosis. Actas Dermosifiliogr 2011;102:623-6.  Back to cited text no. 1
Huerta-Brogeras M, Olmos O, Borbujo J, Hernández-Núñez A, Castaño E, Romero-Maté A, et al. Validation of dermoscopy as a real-time noninvasive diagnostic imaging technique for actinic keratosis. Arch Dermatol 2012;148:1159-64.  Back to cited text no. 2
Uhlenhake EE, Sangueza OP, Lee AD, Jorizzo JL. Spreading pigmented actinic keratosis: A review. J Am Acad Dermatol 2010;63:499-506.  Back to cited text no. 3
Pock L, Drlík L, Hercogová J. Dermatoscopy of pigmented actinic keratosis – A striking similarity to lentigo maligna. Int J Dermatol 2007;46:414-6.  Back to cited text no. 4
Lane H, O'Loughlin S, Powell F, Magee H, Dervan PA. A quantitative immunohistochemical evaluation of lentigo maligna and pigmented solar keratosis. Am J Clin Pathol 1993;100:681-5.  Back to cited text no. 5
James MP, Wells GC, Whimster IW. Spreading pigmented actinic keratoses. Br J Dermatol 1978;98:373-9.  Back to cited text no. 6
Subrt P, Jorizzo JL, Apisarnthanarax P, Head ES, Smith EB. Spreading pigmented actinic keratosis. J Am Acad Dermatol 1983;8:63-7.  Back to cited text no. 7
Dinehart SM, Sanchez RL. Spreading pigmented actinic keratosis. An electron microscopic study. Arch Dermatol 1988;124:680-3.  Back to cited text no. 8
Klinker M, Jonsson N. Simulation of solar lentigo by spreading pigmented actinic keratosis. Acta Derm Venereol 1994;74:406-7.  Back to cited text no. 9
Abudu B, Calame A, Cohen PR. Pigmented actinic keratosis: Case report and review of an uncommon actinic keratosis variant that can mimic melanoma. Cureus 2019;11:e4721.  Back to cited text no. 10
Chung HJ, McGuigan KL, Osley KL, Zendell K, Lee JB. Pigmented solar (actinic) keratosis: An underrecognized collision lesion. J Am Acad Dermatol 2013;68:647-53.  Back to cited text no. 11
Lallas A, Argenziano G, Moscarella E, Longo C, Simonetti V, Zalaudek I. Diagnosis and management of facial pigmented macules. Clin Dermatol 2014;32:94-100.  Back to cited text no. 12
Gupta AK, Paquet M, Villanueva E, Brintnell W. Interventions for actinic keratoses. Cochrane Database Syst Rev 2012;12:CD004415.  Back to cited text no. 13


  [Figure 1], [Figure 2], [Figure 3], [Figure 4]


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