When A Patient Has An Unusual Growth On A Toe

A 43-year-old African-American male presents to the office with an irritated fourth toe with no known trauma to the toe. There is a horny projection of skin coming from the posterior nail fold with a nail-like structure at the tip. It has been present for the past two years and had recently become larger.

The lesion is asymptomatic except for physical inconveniences.
The patient reports that the toe is painful only in shoes. The patient works as a custodian and spends a lot of time on his feet. He has recent onset diabetes of three years but has not been to a podiatrist in the last two years. The patient has no other medical history concerns other than the NIDDM. He denies seizures and other past medical history. There was no family history of any systemic issues, mental retardation or polydactly.
The examination revealed a 1.8 cm long, non-tender, firm, skin-colored growth with a rough surface at the tip projected distally from the proximal nail fold of the toe at the level of the middle phalanx. The growth was in contact with the nail and had caused a longitudinal groove or deformity of the nail plate. The patient was just aware that a piece of skin was causing irritation to the toe. There was no bleeding or ulceration of the growth.
A careful examination revealed no other growths on the other toes or foot. Evaluation of the entire body revealed no other dermatological findings.

Pertinent Diagnostic Considerations
When a patient comes to the office with a growth on the skin, one has to try to classify the lesion in order to aid in the diagnosis. All lesions/ skin tumors can be grouped according to different classification systems. One of the systems looks at histological origin, the age of the patient, location of the lesion and clinical appearance/ topography.1
In terms of histological origin —which is divided into epidermal, mesodermal and nevus cell tumors as well as lymphomas and myeloses — this patient’s lesion fits into the epidermal cell tumor classification.
Some of the more common tumors in adults include: warts, nevi, cysts, skin tags, keloids, lipomas and pyogenic granulomas. In terms of location, the more common skin lesions found on the hands and feet are: warts, nevi, seborrheic keratosis, lentigo, myxoid cyst (proximal nail fold), squamous cell carcinoma, glomus tumor (nail bed), ganglion, acral lentiginous melanoma, pyogenic granuloma, acquired digital fibrokeratoma and traumatic fibroma.1,2

The most important diagnostic factor is clinical appearance or topography since many skin lesions have clinical characteristics common to several lesions. Since the growth in question is basically a raised, skin-colored tumor, the list of the more common lesions encountered includes: warts, skin tags, nevi, cysts, lipomas, keloids and basal cell carcinoma.
The less common ones include: infantile digital fibroma, cutaneous horn, acrochordons, osteochondroma, subungual exostosis, squamous cell carcinoma and superficial acral fibromyxoma. If there is any question as to what the growth really is, one should take a biopsy.

Recognizing The Signs Of An Acquired Periungual Fibrokeratoma
The diagnosis is acquired periungual fibrokeratoma. This condition presents as solitary, elongated or dome-shaped papules with tall finger-like protrusions and a hyperkeratotic surface. The base may have a characteristic collarette of raised skin.2 Most lesions are small and do not exceed 1.5 cm in length or diameter.
In this case, the patient’s lesion was 1.8 cm in length. In regard to acquired periungual fibrokeratoma, the most common sites of occurrence are fingers and toes. However, lesions on the palms and soles can occur. Often, the lesion emerges from beneath the proximal nail fold with a narrow base and hyperkeratotic tip. The lesions may be multiple and grow on the nail plate, causing longitudinal grooves. Occasionally, acquired digital fibrokeratoma may be pedunculated and the surface may appear warty.3,4
The condition occurs solely in adults and is believed to result from trauma, whether it is due to an injury or due to shoe gear. These lesions are more of a cosmetic issue than a painful growth. Clinically similar lesions in children are more likely to represent rudimentary supernumerary digits.5 The condition is benign and surgical excision is curative. When it comes to periungual lesions arising below proximal nail folds, physicians should excise them with due care so as to not damage the matrix, which may result in permanent nail dystrophy.6

A Guide To The Differential Diagnosis

The differential diagnosis of acquired periungual fibrokeratoma includes a variety of the following conditions.
Warts. Warts are very common small tumors of the skin caused by the human papillomavirus. A wart is usually a papillary growth that is slightly raised above the skin surface. One will usually find periungual warts under the nail plate or on the side. They are difficult to treat. There is also a cauliflower-like appearance. In this patient, the soft tissue growth was on top of the nail so this diagnosis was not as likely.
Osteochondroma. This is a benign tumor that contains both bone and cartilage, and usually occurs near the end of a long bone. This tumor is one of the more common benign bone tumors and has a cartilage-capped bony spur. The skin may be irritated on the surface, resulting in bursa formation. No bony component was visible on our radiograph.
Subungual exostosis. A subungual exostosis is an acquired, benign bony tumor that presents as a distal, subungual mass on the toe. It begins as a reactive fibrous growth that develops cartilage and ultimately ossifies. Complete excision remains the treatment of choice. In regard to the patient in this case, there was no obvious bony component on the radiograph.
Periungual fibromas. These are pink, smooth, fibrotic multilobulated nodules that occur around the nail folds and mainly in cases of tuberous sclerosis.7 They are flesh-colored papules that may displace and distort the nail bed. These periungual papules appear in late childhood and may be the sole cutaneous finding in some affected individuals.5,8
The periungual fibromas in tuberous sclerosis are also known as Koenen tumors.
Tuberous sclerosis is a multi-system genetic condition with key features including multiple facial angiofibromas, hypopigmented macules, seizures, cardiac rhabdomyoma and renal lesions. Tuberous sclerosis is the most common neurocutaneous syndrome after neurofibromatosis.9 Dermatologic manifestations may be the only clues to the diagnosis of the disorder, which is also marked by childhood seizures and mental retardation. Characteristic signs of tuberous sclerosis vary widely in severity and can also include hypopigmented “ash leaf spots,” fibrous plaques on the forehead, angiofibromas on the face (adenoma sebaceum), and a shagreen patch on the lower back. In this case, the patient was an adult with no history of seizures or other systemic issues.
Squamous cell carcinoma. This is a common malignant tumor arising from the keratinocytes of the epidermis. The most common clinical picture is a rapidly growing nodule that develops a central ulcer. It can also be a small, slightly raised warty or brownish nodule with hyperkeratosis. It is not commonly found on the foot. However, when any growth appears unusual, one should obtain a biopsy. Squamous cell carcinoma is the most common skin cancer among African-Americans and one study found that 65 percent of these carcinomas occurred in non-sun exposed areas. When it comes to Caucasians, the majority of squamous cell carcinomas are found in sun-exposed areas.10 Squamous cell carcinoma may also be confused with the diagnosis of a “recalcitrant” wart so getting a biopsy is very important.
Aggressive digital papillary adenocarcinoma. Such tumors are rare and arise from skin sweat glands. They usually involve solitary cystic nodules of less than 2 cm. Pain is a frequent presenting complaint. Clinically, these tumors tend to present as solid masses usually on the fingers, toes or adjacent parts of the palms and soles. There is a high rate of local recurrence and these tumors can metastasize.11
In the patient’s case, the periungual fibrokeratoma was not painful and more importantly, the biopsy ruled out an aggressive digital papillary adenocarcinoma.
Acrochordons. An acrochordon is one of the most common benign skin tumors. These lesions are commonly known as skin tags and occasionally fibroepithelial polyps. They often develop in areas of skin friction, which certainly takes place at the tip of the toe. However, these lesions are usually much smaller and not nodule-like. While these lesions are benign, they may be associated with other disease states, occasionally warranting closer examination of the patient for other signs and symptoms.
Rudimentary supernumerary digits. Such digits can clinically appear as miniature accessory digits much like a periungual fibrokeratoma. However, rudimentary supernumerary digits are usually present since birth and are bilateral. In this patient’s case, the growth formed over the past two years. The histological image of these entities is similar with an increase of keratin at the distal edge of the specimen, which can look similar to a nail.
Cutaneous horn. A cutaneous horn usually occurs in sun-exposed areas, particularly the face, nose, forearms and dorsal hands. It is a hyperkeratotic papule with the height greater than one-half the width of the base. Usually a cutaneous horn is several millimeters long. In this patient’s case, the growth was much larger.
Superficial acral fibromyxoma is a rare soft tissue tumor with a predilection for the nail region of the fingers and toes.12 The neoplasm occurs in adults as a solitary, slow-growing mesenchymal mass involving the periungual and subungual areas of the fingers and toes. A histological diagnosis is needed to differentiate this from a periungual fibrokeratoma.

In Conclusion
The biopsy initially ruled the growth as a connective tissue nevus, which means nothing more than a localized malformation of dermal collagen. They are uncommon skin lesions that occur when the deeper layers of the skin do not develop correctly. Based on the clinical picture of this patient, I had some reservation about the diagnosis.
If the pathology reading does not make sense to you, it is your obligation to speak with the pathologist or you may send the slides to another pathologist. This is a common practice. I spoke with the pathologist and met with him in person to go over the case, and show him a photo of the growth in question. After the discussion, he modified his diagnosis to acquired periungual digitial fibrokeratoma. It is very important to provide supporting clinical information to the dermatopathologist in addition to the biopsy specimen.

Dr. Morse is the President of the American Society of Podiatric Dermatology. He is a Fellow of the American College of Foot and Ankle Surgery and the American College of Foot Ankle Orthopedics and Medicine. Dr. Morse is board certified in foot surgery.

References:

1. Hall JC. Sauer’s Manual of Skin Diseases: Eighth Edition. Lippincott Wiliams and Wilkins, Philadelphia, 2000.
2. Bolognia JL, Jorizzo JL, Rapini RP, Ed: Dermatology – Second Edition. Elsevier. Spain. Pp. 1 – 9 and 1033
3. Johnson BL, Moy RL, White GM: Ethnic Skin: Medical and Surgical. Mosby. St. Louis. 1998. Pp.51.
4. Kakurai M, Yamada T, Kiyosawa T, Ohtsuki M, Nakagawa H. Giant acquired digital fibrokeratoma. J Am Acad Dermatol. May 2003;48(5 Suppl):S67-8.
5. Inamadar AC, Palit A, Sampagavi VV, Yelikar BR. Horney projection on hand. Indian J Dermatol Venereol Leprol. 2004;70: 325-326.
6. Kline Satter, E: Acquired Digital Fibrokeratoma in emedicine from web MD, Nov 2007.
7. Braverman IM: Skin Signs of Systemic Disease – Third Edition, WB Saunders Company. Philadelphia. 1998. Pp.548 – 554.
8. Hurst JS, Wilcoski S: Recognizing an Index Case of Tuberous Sclerosis. American Family Physician 2000 Feb 1;61(3): 703-8, 710.
9. Odom RB, James WD, Berger TG: Andrew’s Diseases of the Skin – Ninth Edition. WB Saunders. Philadelphia. 2000.
10. Johnson BL, Moy RL, White GM: Ethnic Skin: Medical and Surgical. Mosby. St. Louis. 1998. Pp.9.
11. Kantrow SM: A 46-Year-Old Man With an Enlarging Finger Nodule. Archives of Pathology and Laboratory Medicine: Vol. 129, No. 8, pp. e179–e180.
12. Meyerle, JH, Keller RA, Krivda SJ: Superficial acral fibromyxoma of the index finger, Dermatology Online Journal 8(2); 22C.

Suggested Reading
13. Kang SB, Lee JY, Cho BK, Houh W: Two Cases of Acquired Periungual Fibrokeratoma. Korean J Dermatol. 1987 Dec;25(6);863-867.
14. Saito S, Ishikawa K: Acquired Periungual Fibrokeratoma With Accessory Germinal Matrix. Journal of Hand Surgery.27(6): 549-555, 2002.

**i**For a related article, see “Treating Difficult Nails In Diabetic Patients” in the March 2006 issue of Podiatry Today.
**i**For other articles, please visit the archives at www.podiatrytoday.com.