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CORRESPONDENCE Table of Contents  
Ahead of print publication
Subungual squamous cell carcinoma in situ presenting as longitudinal melanonychia


 Department of Dermatology, Kaohsiung Chang Gung Memorial Hospital and Chang Gung University College of Medicine, Kaohsiung, Taiwan

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Date of Submission22-Mar-2022
Date of Decision06-Jun-2022
Date of Acceptance28-Jun-2022
Date of Web Publication03-Nov-2022
 


How to cite this URL:
Hou YL, Liu KL. Subungual squamous cell carcinoma in situ presenting as longitudinal melanonychia. Dermatol Sin [Epub ahead of print] [cited 2022 Nov 28]. Available from: https://www.dermsinica.org/preprintarticle.asp?id=360449




Dear Editor,

Subungual squamous cell carcinoma (SCC) and in situ (Bowen's disease) are the most common malignant neoplasms of the nail unit, with various clinical manifestations. We herein report a case of subungual SCC in situ presenting as longitudinal melanonychia, which is a rare clinical finding of subungual SCC and SCC in situ.

A 47-year-old man presented with a brownish streak on the lateral aspect of his right index fingernail ongoing for 4 months. He denied trauma, radiation, or contact history with chemical agents. The patient had underlying diseases including diabetes mellitus, hypertension, and anxiety disorder.

Physical examination showed a 1.5 mm-in-width brownish longitudinal melanonychia with color variation and partial hyperkeratosis on the lateral aspect of the right index fingernail, without other nail deformities [Figure 1]a. Dermoscopy revealed a heterogeneous brownish-to-blackish-colored longitudinal streak with a normal lateral nail fold [Figure 1]b. The patient underwent a longitudinal incisional biopsy of the nail bed. Histopathological examination revealed neoplastic growth of squamous epithelial cells bearing pleomorphic and hyperchromatic nuclei confined to the epidermis [Figure 2]a. Immunohistochemical staining for p16 showed diffuse positivity in neoplastic cells [Figure 2]b. The patient was diagnosed with subungual SCC in situ. Wide excision with a 3 mm surgical margin and nail plate removal were subsequently performed. The wound was repaired using a full-thickness skin graft harvested from the thenar region. Histopathological result was compatible with the diagnosis of subungual SCC in situ. The patient's wound recovered well after 1 month of follow-up.
Figure 1: (a) Physical examination showing brownish longitudinal melanonychia with color variatioan and partial hyperkeratosis on the fingernail. (b) Dermoscopy reveals a heterogeneous brownish to blackish-colored longitudinal streak with a normal lateral nail fold (the picture of dermoscopy was taken before wide excision).

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Figure 2: (a) The longitudinal incisional biopsy of the nail bed showing neoplastic growth of squamous epithelial cells with pleomorphic and hyperchromatic nuclei confined in the epidermis (H and E stain, ×200). (b) Immunohistochemistry staining of p16 showing diffuse positivity in the neoplastic cells (IHC, ×200).

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Subungual SCC and in situ (Bowen's disease) are rare although they are the most common malignant tumors of the nail unit and mostly occur on the fingernails of elderly men.[1] Various clinical manifestations of subungual SCC and in situ have been reported including pain, swelling, warty appearance, subungual hyperkeratosis, onycholysis, nail plate destruction, nail bed erosion, nodular appearance, and longitudinal melanonychia.[1],[2] Our case involved a middle-aged man with brownish-to-blackish-colored longitudinal melanonychia on the index fingernail diagnosed as subungual SCC in situ. In a retrospective study including 20 cases of nail SCC, the results showed that most cases of longitudinal melanonychia were SCC in situ.[2]

Due to its heterogeneous clinical appearance, subungual SCC can be misdiagnosed as warts, paronychia, onychomycosis, pyogenic granuloma, onychomatricoma, fibrokeratoma, keratoacanthoma, and melanoma.[3] High-risk human papillomavirus (HPV) infection (such as types 16 and 56), chemical contact, trauma, radiation, congenital conditions, and immunosuppression are thought to be the potential predisposing factors for SCC in the nail unit.[4] The expression of p16 tumor suppressor may be associated with HPV infection in cases of SCC and in situ. In some pathologically challenging cases, p16 expression and identification of palisading basal cell-sparing patterns can be useful for supporting the diagnosis of Bowen's disease.[5] In our case, immunohistochemical staining of p16 showed diffuse positivity, which indicates a correlation with HPV infection and strengthens the diagnosis of Bowen's disease.

There are several possible etiologies of melanonychia, such as lentigo, melanocytic nevi, subungual hematoma, infection, drugs, inflammatory diseases, mechanical factors, keratinocyte nail tumors (e.g., Bowen's disease, SCC, onychopapilloma, and rarely onychomatricoma), and melanoma.[6] The mechanism of increased melanin pigment deposition in subungual SCC remains unclear although some believe that melanocytic colonization is a hypothesis.[7] However, the histopathological results of our case showed only increased melanin pigment without evidence of melanocytic proliferation in the lesion. In the diagnosis of melanonychia, it is important to differentiate benign melanocytic lesions from malignant lesions, such as melanoma, Bowen's disease, and SCC. The pattern of melanonychia in a nail matrix nevus or subungual lentigo is generally characterized by a pigmented band with a regular thickness, whereas melanonychia in cases of nail SCC shows different widths along the band with mild-to-moderate hyperkeratotic changes.[2]

Complete surgical excision with wide excision or Mohs micrographic surgery is considered the first-line treatment for nail SCC, with low recurrence rates.[8] Mohs micrographic surgery may be superior to wide excision in some cases, considering the intraoperative histological confirmation of tissue invasion. Ampu tation is a standard treatment for bone invasion.[8] Conservative treatments, such as topical therapies, radiation therapy, cryotherapy, and curettage, can also be considered alternative treatments based on the clinical circumstances and patient preferences. Our patient underwent wide excision with a 3 mm surgical margin and full-thickness skin graft repair. No surgical complications were observed, with good wound healing after 1 month of follow-up.

In conclusion, we present the case of unusual clinical manifestation of longitudinal melanonychia with subungual SCC in situ. This case reminds us that subungual SCC and SCC in situ should be considered differential diagnoses of longitudinal melanonychia.

Ethical approval

This study was approved by the institutional review board of Chang Gung Medical Foundation (NO. 202200314B0). The patient consent is waived by the IRB.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Starace M, Alessandrini A, Dika E, Piraccini BM. Squamous cell carcinoma of the nail unit. Dermatol Pract Concept 2018;8:238-44.  Back to cited text no. 1
    
2.
Lee J, Shin DM, Oh SJ, Park JH, Lee D. A retrospective study of nail squamous cell carcinoma at a single tertiary center: A relationship between longitudinal melanonychia and the depth of invasion. J Am Acad Dermatol 2022;S0190-9622(22)00192-X.  Back to cited text no. 2
    
3.
Dika E, Starace M, Patrizi A, Fanti PA, Piraccini BM. Squamous cell carcinoma of the nail unit: A clinical histopathologic study and a proposal for classification. Dermatol Surg 2019;45:365-70.  Back to cited text no. 3
    
4.
Dijksterhuis A, Friedeman E, van der Heijden B. Squamous cell carcinoma of the nail unit: Review of the literature. J Hand Surg Am 2018;43:374-9.e2.  Back to cited text no. 4
    
5.
Hong R. The utility of p16 immunostaining in cutaneous keratinocytic lesion. Med Biol Sci Eng 2019;2:40-5.  Back to cited text no. 5
    
6.
Alessandrini A, Dika E, Starace M, Chessa MA, Piraccini BM. Diagnosis of melanonychia. Dermatol Clin 2021;39:255-67.  Back to cited text no. 6
    
7.
Ishida M, Iwai M, Yoshida K, Kagotani A, Okabe H. Subungual pigmented squamous cell carcinoma presenting as longitudinal melanonychia: A case report with review of the literature. Int J Clin Exp Pathol 2014;7:844-7.  Back to cited text no. 7
    
8.
Ning AY, Levoska MA, Zheng DX, Carroll BT, Wong CY. Treatment options and outcomes for squamous cell carcinoma of the nail unit: A systematic review. Dermatol Surg 2022;48:267-73.  Back to cited text no. 8
    

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Correspondence Address:
Kwei-Lan Liu,
Department of Dermatology, Kaohsiung Chang Gung Memorial Hospital and Chang Gung University College of Medicine, No. 123, DAPI Road, Niaosong District, Kaohsiung City 83301
Taiwan
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/1027-8117.360449



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