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Pigmented Onychomatricoma: A Rare Pigmented Nail Unit Tumor Presenting as Longitudinal Melanonychia That Has Potential for Misdiagnosis as Melanoma
The Journal of Foot & Ankle Surgery 54 (2015) 723–725
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Pigmented Onychomatricoma: A Rare Pigmented Nail Unit Tumor Presenting as Longitudinal Melanonychia That Has Potential for Misdiagnosis as Melanoma Jacob Wynes, DPM, MS, AACFAS 1, Karolyn A. Wanat, MD 2, Auris Huen, MD, PharmD 3, Alan J. Mlodzienski, DPM, FACFAS 4, Adam I. Rubin, MD 5 1
Fellow, Foot and Ankle Deformity Correction, International Center for Limb Lengthening, Rubin Institute for Advanced Orthopedics, Sinai Hospital, Baltimore, MD Assistant Professor, Department of Dermatology, University of Iowa, Iowa City, IA Second Year Resident, Department of Dermatology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 4 Director of Residency, Division of Podiatric Surgery, Penn Presbyterian Medical Center, Philadelphia, PA 5 Assistant Professor, Department of Dermatology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 2 3
a r t i c l e i n f o
a b s t r a c t
Level of Clinical Evidence: 4
Pigmented onychomatricoma is a rare nail unit tumor that can clinically mimic nail unit melanoma. We report the case of a 63-year-old male with new-onset longitudinal melanonychia involving his right second toe. An excisional biopsy was performed and demonstrated pigmented onychomatricoma. We present this case to alert clinicians of this rare nail unit tumor and the importance of clinicopathologic correlation to avoid misdiagnosis. Ó 2015 by the American College of Foot and Ankle Surgeons. All rights reserved.
Keywords: biopsy melanoma nail onychomatricoma tumor
The evaluation of longitudinal melanonychia involving a single nail unit often requires a biopsy to establish a specific diagnosis, because the differential diagnosis includes various causes such as a melanotic macule or subungual melanoma. In these cases, communication between the submitting clinician and the pathologist is essential for proper orientation of the specimen and for correlation of the histopathologic findings. We present the case of a 63-year-old male with clinical features concerning for subungual melanoma that was initially difficult to diagnose and prompted additional interdisciplinary communication and implementation of specific histopathologic techniques to confirm the diagnosis. Case Report A 63-year-old male with no personal or family history of melanoma but with a history of multiple nevi, lentigines, and seborrheic keratoses presented with new-onset monodactylous longitudinal Financial Disclosure: None reported. Conflict of Interest: None reported. Address correspondence to: Jacob Wynes, DPM, MS, AACFAS, Foot and Ankle Deformity Correction, International Center for Limb Lengthening, Rubin Institute for Advanced Orthopedics, Sinai Hospital, 2401 West Belvedere Avenue, Baltimore, MD 21215. E-mail address: [email protected] (J. Wynes).
melanonychia affecting the right second toe nail unit that had developed during the previous 12 months. On physical examination, a tan, brown linear streak was present, extending the length of the nail plate, with well-demarcated borders measuring 3.5 mm in width. An 0.8 mm extension of the pigmentation was present on the cuticle and proximal nail fold, consistent with Hutchinson’s sign (Fig. 1). He had no history of trauma to the affected nail unit or any inciting event. The patient was referred to podiatry for evaluation and treatment. A longitudinal excisional biopsy of the hyperpigmented band was performed to obtain an elliptical sample that included the nail plate, nail bed, and hyperpigmented proximal nail fold. At 1 year of follow-up, the patient’s biopsy site had healed uneventfully with no evidence of recurrence. The unoriented specimen was sectioned using transverse sectioning (“bread loafing”), which demonstrated unremarkable skin with hyperkeratotic keratin pearls and no explanation for the clinical pigmentation. After a failure to adequately correlate the clinical findings with the pathologic features noted, the specimen was reoriented for additional histopathologic evaluation. The pathology specimen showed areas of nail unit epithelial projections demonstrating papillomatosis and an associated thickened nail plate. These epithelial projections were closely associated with a fibrous proliferation in the dermis (Fig. 2A) that was highlighted using CD34 immunoperoxidase staining (Fig. 2B). Increased pigmentation of the nail unit epithelium and nail plate was highlighted using Fontana-Masson staining. A
1067-2516/$ - see front matter Ó 2015 by the American College of Foot and Ankle Surgeons. All rights reserved. http://dx.doi.org/10.1053/j.jfas.2014.05.013
724
J. Wynes et al. / The Journal of Foot & Ankle Surgery 54 (2015) 723–725
Fig. 1. Clinical photograph showing longitudinal melanonychia extending to involve the proximal nail fold (pseudo-Hutchinson’s sign). The overlying nail plate was also thickened, with longitudinal ridges.
normal number of melanocytes were present in the specimen. The presence of a CD34-positive fibroepithelial tumor with these histopathologic features in the absence of a melanocytic lesion was consistent with a diagnosis of pigmented onychomatricoma. Discussion Onychomatricoma is rare benign fibroepithelial tumor of the nail unit originally described by Baran and Kint in 1992 (1). It has typically presented in males and females equally, with an average age at diagnosis of 48 (range 4 to 72) years. It appears to have a greater predilection for the finger nail than for the toe nail (2:1) (1–4). Previous reports have suggested possible underreporting of toe involvement (relative to the fingers) (5). The first description in the pediatric population was reported by Piraccini et al (3) in 2007 in a
4-year-old female that was coincident with onychomycosis. Common clinical findings have included thickening of the nail plate with ridging and xanthonychia isolated to a linear band. Onychomatricoma can be associated with onychomycosis; thus, it is important to consider this diagnosis in a patient diagnosed with onychomycosis who has not responded to therapy (6,7). Treatment of onychomycosis (with culture and sensitivity testing, if necessary) should occur initially. If no response occurs, one should consider a nail bed, plate, or matrix biopsy. When directly evaluating an affected nail, small holes can often be seen, sometimes described as a “wormwood appearance” (5,8). Splinter hemorrhages can also be seen (3,9). Histologic examination is necessary to establish the diagnosis. The key histopathologic findings include both a fibrous and an epithelial component of the tumor, and soft tissue projections of the tumor can often be seen within the nail plate that can be visualized as small holes with an epithelial lining (1,10). Dermoscopy can also aid the clinician in deciding whether to biopsy a lesion and allows for precise visualization of the pigmented lines, which can vary in color, width, and spacing (11). Recently, the use of nail clippings to establish the diagnosis of an onychomatricoma has been shown to be useful. A combination of periodic acid-Schiff analysis, hematoxylin and eosin staining, and anti-pancytokeratin antibody MNF116 staining was used to highlight the honeycomb cavities with epithelial tumor projections (9). Electron microscopy has demonstrated a cytoplasmic rim containing mitochondria and tonofilaments within the basal cell layer (12) of the proximal zone of the onychomatricoma. In addition, recent reports have used high-frequency ultrasonography, similar to that used for identification of other nail bed tumors; however, skilled interpretation would be required, despite the appearance of characteristic hyperechoic linear dots (13). Pigmented onychomatricoma is a variant of onychomatricoma that is extremely rare, with only 3 cases previously described in the published data (6). The clinical characteristics of the reported cases are summarized in Table. Similar to the present case, the other 3 cases of pigmented onychomatricomas had an insidious onset and were asymptomatic. The reported cases presented as a linear,
Fig. 2. Histopathologic evaluation. (A) On low power, the epithelial projections and thickened plate can be observed (hematoxylin and eosin stain, original magnification 40). (B) Pigmentation can be visualized within the nail plate and within the epidermis (hematoxylin and eosin stain, original magnification 100) that was associated with (C) a fibrous proliferation within the dermis (hematoxylin and eosin stain, original magnification 200). (D) This fibrous proliferation was highlighted by a CD34 immunostain (original magnification 200).
J. Wynes et al. / The Journal of Foot & Ankle Surgery 54 (2015) 723–725
725
Table Summary of reported pigmented onychomatricoma cases Patient No.
Age (yr)
Sex
Location
Clinical Features
1
64
Male
Left second toe
2
50
Male
Left fourth toe
3 Present patient
24 63
Female Male
Left third toe Right second toe
Longitudinal band with nail thickened but not hard or crumbly History of Trichophyton mentagrophytes onychomycosis treated with terbinafine 2 Longitudinal bands at edge of partially thickened, yellowish nail plate Proximal nail fold edema, painless History of Trichophyton rubrum onychomycosis treated with terbinafine and topical amorolfine Longitudinal melanonychia on initial presentation, developing distal fissure and yellow discoloration at edge 1 yr later Longitudinal melanonychia with extension of pigmentation on cuticle and proximal nail fold (pseudo-Hutchinson’s sign)
Cases 1 to 3 reported by Fayol et al (6).
well-demarcated, hyperpigmented band with associated nail plate thickening. A few cases also had a yellow discoloration at the edge of hyperpigmentation that helped raised suspicion for onychomatricoma. Our patient did not have a yellow discoloration but shared similar clinical features, with exception of the prominent discoloration and extension of the pigmentation onto the proximal nail fold, clinically mimicking a subungual melanoma. The clinical differential diagnosis for monodactylous longitudinal melanonychia with nail thickening could include subungual melanoma, traumatic nail changes associated with a hematoma, pigmented Bowen’s disease, pigmented onychomycosis, and onychocytic matricoma (1,14,15). This broad clinical differential diagnosis necessitates histopathologic examination and a specimen of adequate dimensions with appropriate sectioning. A piece of nail will not be always longitudinal, and, if it has been sectioned horizontally or “breadloafed” (which will be the case for most surgical specimens), the results can be affected. When evaluating longitudinal melanonychia, the specimens should be oriented by the surgeon and then sectioned longitudinally to ensure evaluation of the various anatomic subunits of the nail unit, including the nail matrix and nail bed. Commonly, immunohistochemical techniques are used to diagnose an onychomatricoma. CD34 is a marker found on a variety of hematopoietic, mesenchymal, and follicular outer sheath cells. In onychomatricoma, CD34 staining will typically be strong and will be found in the dermal component of the tumor. In the evaluation of an onychomatricoma sample, it is reasonable to use other stains such as S100 and pancytokeratin for additional evaluation of the sample. Cytokeratin immunoperoxidase stains can be helpful to confirm the diagnosis in longitudinal sections and to identify the epithelial component of the lesion in a nail clipping (9). As in the case presented, appropriate consultation with a dermatopathologist or nail unit specialist is often necessary to obtain the most accurate diagnosis when clinical suspicion is high. In conclusion, we have reported a case of a rare nail unit tumor, a pigmented onychomatricoma. Given the potential severity of an undiagnosed malignancy, clinicians should be aware of this tumor and the other potential nail unit tumors that can present with longitudinal
melanonychia and the importance of interdisciplinary communication when evaluating nail unit hyperpigmentation. Just as in the present case, clinical suspicion, coupled with pathologic correlation, appropriate processing measures, and communication, provided excellent continuity of medical care with eventual establishment of a diagnosis of pigmented OM. References 1. Baran R, Kint A. Onychomatrixoma: filamentous tufted tumour in the matrix of a funnel-shaped nail: a new entity (report of three cases). Br J Dermatol 126:510– 515, 1992. 2. Perrin C, Goettmann S, Baran R. Onychomatricoma: clinical and histopathologic findings in 12 cases. J Am Acad Dermatol 39(4 Pt 1):560–564, 1998. 3. Piraccini BM, Antonucci A, Rech G, Starace M, Misciali C, Tosti A. Onychomatricoma: first description in a child. Pediatr Dermatol 24:46–48, 2007. 4. Gaertner EM, Gordon M, Reed T. Onychomatricoma: case report of an unusual subungual tumor with literature review. J Cutan Pathol 36(suppl 1)):66–69, 2009. 5. Becerro de Bengoa R, Gates JR, Losa Iglesias ME, Alija Martinez B. Rare toenail onychomatricoma: surgical resolution of five cases. Dermatol Surg 37:709–711, 2011. 6. Fayol J, Baran R, Perrin C, Labrousse F. Onychomatricoma with misleading features. Acta Derm Venereol 80:370–372, 2000. 7. Goutos I, Furniss D, Smith GD. Onychomatricoma: an unusual case of ungual pathology. Case report and review of the literature. J Plast Reconstr Aesthet Surg 63:e54–e57, 2010. 8. Perrin C, Baran R, Balaguer T, Chignon-Sicard B, Cannata GE, Petrella T, Michiels JF. Onychomatricoma: new clinical and histological features. A review of 19 tumors. Am J Dermatopathol 32:1–8, 2010. 9. Miteva M, de Farias DC, Zaiac M, Romanelli P, Tosti A. Nail clipping diagnosis of onychomatricoma. Arch Dermatol 147:1117–1118, 2011. 10. Perrin C, Baran R, Pisani A, Ortonne JP, Michiels JF. The onychomatricoma: additional histologic criteria and immunohistochemical study. Am J Dermatopathol 24:199–203, 2002. 11. Adigun CG, Scher RK. Longitudinal melanonychia: when to biopsy and is dermoscopy helpful? Dermatol Ther 25:491–497, 2012. 12. Kint A, Baran R, Geerts ML. The onychomatricoma: an electron microscopic study. J Cutan Pathol 24:183–188, 1997. 13. Soto R, Wortsman X, Corredoira Y. Onychomatricoma: clinical and sonographic findings. Arch Dermatol 145:1461–1462, 2009. 14. Finch J, Arenas R, Baran R. Fungal melanonychia. J Am Acad Dermatol 66:830–841, 2012. 15. Perrin C, Cannata GE, Bossard C, Grill JM, Ambrossetti D, Michiels JF. Onychocytic matricoma presenting as pachymelanonychia longitudinal: a new entity (report of five cases). Am J Dermatopathol 34:54–59, 2012.
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Pigmented Onychomatricoma: A Rare Pigmented Nail Unit Tumor Presenting as Longitudinal Melanonychia That Has Potential for Misdiagnosis as Melanoma Jacob Wynes, DPM, MS, AACFAS 1, Karolyn A. Wanat, MD 2, Auris Huen, MD, PharmD 3, Alan J. Mlodzienski, DPM, FACFAS 4, Adam I. Rubin, MD 5 1
Fellow, Foot and Ankle Deformity Correction, International Center for Limb Lengthening, Rubin Institute for Advanced Orthopedics, Sinai Hospital, Baltimore, MD Assistant Professor, Department of Dermatology, University of Iowa, Iowa City, IA Second Year Resident, Department of Dermatology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 4 Director of Residency, Division of Podiatric Surgery, Penn Presbyterian Medical Center, Philadelphia, PA 5 Assistant Professor, Department of Dermatology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 2 3
a r t i c l e i n f o
a b s t r a c t
Level of Clinical Evidence: 4
Pigmented onychomatricoma is a rare nail unit tumor that can clinically mimic nail unit melanoma. We report the case of a 63-year-old male with new-onset longitudinal melanonychia involving his right second toe. An excisional biopsy was performed and demonstrated pigmented onychomatricoma. We present this case to alert clinicians of this rare nail unit tumor and the importance of clinicopathologic correlation to avoid misdiagnosis. Ó 2015 by the American College of Foot and Ankle Surgeons. All rights reserved.
Keywords: biopsy melanoma nail onychomatricoma tumor
The evaluation of longitudinal melanonychia involving a single nail unit often requires a biopsy to establish a specific diagnosis, because the differential diagnosis includes various causes such as a melanotic macule or subungual melanoma. In these cases, communication between the submitting clinician and the pathologist is essential for proper orientation of the specimen and for correlation of the histopathologic findings. We present the case of a 63-year-old male with clinical features concerning for subungual melanoma that was initially difficult to diagnose and prompted additional interdisciplinary communication and implementation of specific histopathologic techniques to confirm the diagnosis. Case Report A 63-year-old male with no personal or family history of melanoma but with a history of multiple nevi, lentigines, and seborrheic keratoses presented with new-onset monodactylous longitudinal Financial Disclosure: None reported. Conflict of Interest: None reported. Address correspondence to: Jacob Wynes, DPM, MS, AACFAS, Foot and Ankle Deformity Correction, International Center for Limb Lengthening, Rubin Institute for Advanced Orthopedics, Sinai Hospital, 2401 West Belvedere Avenue, Baltimore, MD 21215. E-mail address: [email protected] (J. Wynes).
melanonychia affecting the right second toe nail unit that had developed during the previous 12 months. On physical examination, a tan, brown linear streak was present, extending the length of the nail plate, with well-demarcated borders measuring 3.5 mm in width. An 0.8 mm extension of the pigmentation was present on the cuticle and proximal nail fold, consistent with Hutchinson’s sign (Fig. 1). He had no history of trauma to the affected nail unit or any inciting event. The patient was referred to podiatry for evaluation and treatment. A longitudinal excisional biopsy of the hyperpigmented band was performed to obtain an elliptical sample that included the nail plate, nail bed, and hyperpigmented proximal nail fold. At 1 year of follow-up, the patient’s biopsy site had healed uneventfully with no evidence of recurrence. The unoriented specimen was sectioned using transverse sectioning (“bread loafing”), which demonstrated unremarkable skin with hyperkeratotic keratin pearls and no explanation for the clinical pigmentation. After a failure to adequately correlate the clinical findings with the pathologic features noted, the specimen was reoriented for additional histopathologic evaluation. The pathology specimen showed areas of nail unit epithelial projections demonstrating papillomatosis and an associated thickened nail plate. These epithelial projections were closely associated with a fibrous proliferation in the dermis (Fig. 2A) that was highlighted using CD34 immunoperoxidase staining (Fig. 2B). Increased pigmentation of the nail unit epithelium and nail plate was highlighted using Fontana-Masson staining. A
1067-2516/$ - see front matter Ó 2015 by the American College of Foot and Ankle Surgeons. All rights reserved. http://dx.doi.org/10.1053/j.jfas.2014.05.013
724
J. Wynes et al. / The Journal of Foot & Ankle Surgery 54 (2015) 723–725
Fig. 1. Clinical photograph showing longitudinal melanonychia extending to involve the proximal nail fold (pseudo-Hutchinson’s sign). The overlying nail plate was also thickened, with longitudinal ridges.
normal number of melanocytes were present in the specimen. The presence of a CD34-positive fibroepithelial tumor with these histopathologic features in the absence of a melanocytic lesion was consistent with a diagnosis of pigmented onychomatricoma. Discussion Onychomatricoma is rare benign fibroepithelial tumor of the nail unit originally described by Baran and Kint in 1992 (1). It has typically presented in males and females equally, with an average age at diagnosis of 48 (range 4 to 72) years. It appears to have a greater predilection for the finger nail than for the toe nail (2:1) (1–4). Previous reports have suggested possible underreporting of toe involvement (relative to the fingers) (5). The first description in the pediatric population was reported by Piraccini et al (3) in 2007 in a
4-year-old female that was coincident with onychomycosis. Common clinical findings have included thickening of the nail plate with ridging and xanthonychia isolated to a linear band. Onychomatricoma can be associated with onychomycosis; thus, it is important to consider this diagnosis in a patient diagnosed with onychomycosis who has not responded to therapy (6,7). Treatment of onychomycosis (with culture and sensitivity testing, if necessary) should occur initially. If no response occurs, one should consider a nail bed, plate, or matrix biopsy. When directly evaluating an affected nail, small holes can often be seen, sometimes described as a “wormwood appearance” (5,8). Splinter hemorrhages can also be seen (3,9). Histologic examination is necessary to establish the diagnosis. The key histopathologic findings include both a fibrous and an epithelial component of the tumor, and soft tissue projections of the tumor can often be seen within the nail plate that can be visualized as small holes with an epithelial lining (1,10). Dermoscopy can also aid the clinician in deciding whether to biopsy a lesion and allows for precise visualization of the pigmented lines, which can vary in color, width, and spacing (11). Recently, the use of nail clippings to establish the diagnosis of an onychomatricoma has been shown to be useful. A combination of periodic acid-Schiff analysis, hematoxylin and eosin staining, and anti-pancytokeratin antibody MNF116 staining was used to highlight the honeycomb cavities with epithelial tumor projections (9). Electron microscopy has demonstrated a cytoplasmic rim containing mitochondria and tonofilaments within the basal cell layer (12) of the proximal zone of the onychomatricoma. In addition, recent reports have used high-frequency ultrasonography, similar to that used for identification of other nail bed tumors; however, skilled interpretation would be required, despite the appearance of characteristic hyperechoic linear dots (13). Pigmented onychomatricoma is a variant of onychomatricoma that is extremely rare, with only 3 cases previously described in the published data (6). The clinical characteristics of the reported cases are summarized in Table. Similar to the present case, the other 3 cases of pigmented onychomatricomas had an insidious onset and were asymptomatic. The reported cases presented as a linear,
Fig. 2. Histopathologic evaluation. (A) On low power, the epithelial projections and thickened plate can be observed (hematoxylin and eosin stain, original magnification 40). (B) Pigmentation can be visualized within the nail plate and within the epidermis (hematoxylin and eosin stain, original magnification 100) that was associated with (C) a fibrous proliferation within the dermis (hematoxylin and eosin stain, original magnification 200). (D) This fibrous proliferation was highlighted by a CD34 immunostain (original magnification 200).
J. Wynes et al. / The Journal of Foot & Ankle Surgery 54 (2015) 723–725
725
Table Summary of reported pigmented onychomatricoma cases Patient No.
Age (yr)
Sex
Location
Clinical Features
1
64
Male
Left second toe
2
50
Male
Left fourth toe
3 Present patient
24 63
Female Male
Left third toe Right second toe
Longitudinal band with nail thickened but not hard or crumbly History of Trichophyton mentagrophytes onychomycosis treated with terbinafine 2 Longitudinal bands at edge of partially thickened, yellowish nail plate Proximal nail fold edema, painless History of Trichophyton rubrum onychomycosis treated with terbinafine and topical amorolfine Longitudinal melanonychia on initial presentation, developing distal fissure and yellow discoloration at edge 1 yr later Longitudinal melanonychia with extension of pigmentation on cuticle and proximal nail fold (pseudo-Hutchinson’s sign)
Cases 1 to 3 reported by Fayol et al (6).
well-demarcated, hyperpigmented band with associated nail plate thickening. A few cases also had a yellow discoloration at the edge of hyperpigmentation that helped raised suspicion for onychomatricoma. Our patient did not have a yellow discoloration but shared similar clinical features, with exception of the prominent discoloration and extension of the pigmentation onto the proximal nail fold, clinically mimicking a subungual melanoma. The clinical differential diagnosis for monodactylous longitudinal melanonychia with nail thickening could include subungual melanoma, traumatic nail changes associated with a hematoma, pigmented Bowen’s disease, pigmented onychomycosis, and onychocytic matricoma (1,14,15). This broad clinical differential diagnosis necessitates histopathologic examination and a specimen of adequate dimensions with appropriate sectioning. A piece of nail will not be always longitudinal, and, if it has been sectioned horizontally or “breadloafed” (which will be the case for most surgical specimens), the results can be affected. When evaluating longitudinal melanonychia, the specimens should be oriented by the surgeon and then sectioned longitudinally to ensure evaluation of the various anatomic subunits of the nail unit, including the nail matrix and nail bed. Commonly, immunohistochemical techniques are used to diagnose an onychomatricoma. CD34 is a marker found on a variety of hematopoietic, mesenchymal, and follicular outer sheath cells. In onychomatricoma, CD34 staining will typically be strong and will be found in the dermal component of the tumor. In the evaluation of an onychomatricoma sample, it is reasonable to use other stains such as S100 and pancytokeratin for additional evaluation of the sample. Cytokeratin immunoperoxidase stains can be helpful to confirm the diagnosis in longitudinal sections and to identify the epithelial component of the lesion in a nail clipping (9). As in the case presented, appropriate consultation with a dermatopathologist or nail unit specialist is often necessary to obtain the most accurate diagnosis when clinical suspicion is high. In conclusion, we have reported a case of a rare nail unit tumor, a pigmented onychomatricoma. Given the potential severity of an undiagnosed malignancy, clinicians should be aware of this tumor and the other potential nail unit tumors that can present with longitudinal
melanonychia and the importance of interdisciplinary communication when evaluating nail unit hyperpigmentation. Just as in the present case, clinical suspicion, coupled with pathologic correlation, appropriate processing measures, and communication, provided excellent continuity of medical care with eventual establishment of a diagnosis of pigmented OM. References 1. Baran R, Kint A. Onychomatrixoma: filamentous tufted tumour in the matrix of a funnel-shaped nail: a new entity (report of three cases). Br J Dermatol 126:510– 515, 1992. 2. Perrin C, Goettmann S, Baran R. Onychomatricoma: clinical and histopathologic findings in 12 cases. J Am Acad Dermatol 39(4 Pt 1):560–564, 1998. 3. Piraccini BM, Antonucci A, Rech G, Starace M, Misciali C, Tosti A. Onychomatricoma: first description in a child. Pediatr Dermatol 24:46–48, 2007. 4. Gaertner EM, Gordon M, Reed T. Onychomatricoma: case report of an unusual subungual tumor with literature review. J Cutan Pathol 36(suppl 1)):66–69, 2009. 5. Becerro de Bengoa R, Gates JR, Losa Iglesias ME, Alija Martinez B. Rare toenail onychomatricoma: surgical resolution of five cases. Dermatol Surg 37:709–711, 2011. 6. Fayol J, Baran R, Perrin C, Labrousse F. Onychomatricoma with misleading features. Acta Derm Venereol 80:370–372, 2000. 7. Goutos I, Furniss D, Smith GD. Onychomatricoma: an unusual case of ungual pathology. Case report and review of the literature. J Plast Reconstr Aesthet Surg 63:e54–e57, 2010. 8. Perrin C, Baran R, Balaguer T, Chignon-Sicard B, Cannata GE, Petrella T, Michiels JF. Onychomatricoma: new clinical and histological features. A review of 19 tumors. Am J Dermatopathol 32:1–8, 2010. 9. Miteva M, de Farias DC, Zaiac M, Romanelli P, Tosti A. Nail clipping diagnosis of onychomatricoma. Arch Dermatol 147:1117–1118, 2011. 10. Perrin C, Baran R, Pisani A, Ortonne JP, Michiels JF. The onychomatricoma: additional histologic criteria and immunohistochemical study. Am J Dermatopathol 24:199–203, 2002. 11. Adigun CG, Scher RK. Longitudinal melanonychia: when to biopsy and is dermoscopy helpful? Dermatol Ther 25:491–497, 2012. 12. Kint A, Baran R, Geerts ML. The onychomatricoma: an electron microscopic study. J Cutan Pathol 24:183–188, 1997. 13. Soto R, Wortsman X, Corredoira Y. Onychomatricoma: clinical and sonographic findings. Arch Dermatol 145:1461–1462, 2009. 14. Finch J, Arenas R, Baran R. Fungal melanonychia. J Am Acad Dermatol 66:830–841, 2012. 15. Perrin C, Cannata GE, Bossard C, Grill JM, Ambrossetti D, Michiels JF. Onychocytic matricoma presenting as pachymelanonychia longitudinal: a new entity (report of five cases). Am J Dermatopathol 34:54–59, 2012.