Trichodiscoma

Are You Confident of the Diagnosis?

What you should be alert for in the history

The diagnosis of trichodiscoma is considered when a solitary skin-colored lesion that is smooth and firm, but is otherwise asymptomatic, is present on the face, trunk, or thighs. If multiple such lesions appear and there is a family history of it, one should be suspicious of Birt-Hogg-Dubé syndrome.

Characteristic findings on physical examination

Trichodiscomas can be solitary or multiple. In both cases, they are ivory or flesh-colored discrete smooth dome-shaped slightly firm papules that range in size from 2-5mm. Trichodiscomas typically have a predilection for the face, thighs, and trunk.

Expected results of diagnostic studies

On histology, trichodiscomas are located in the dermis and are tumors composed of mucinous and richly vascularized dermal tissue containing both collagen and elastic fibers. Hair follicles are almost always present at the periphery of the neoplasm. Melanin granules are present in scattered small fusiform and stellate cells throughout the tumor stroma, and thick myelinated nerve fibers are occasionally present at the base of the lesion. There is an absence of Merkel cells, which suggests that trichodiscomas originate from the fibrovascular component of the hair disk.

On immunohistochemistry, the stroma of trichodiscomas express CD34 antigen.

Diagnosis confirmation

The differential diagnosis includes other follicular tumors, such as trichoepithelioma and its variant desmoplastic trichoepithelioma, as well as trichofolliculoma. These can be differentiated based on histology.

Trichodiscomas can also resemble basal cell carcinoma. Basal cell carcinomas can be differentiated from trichodiscomas on histology. Basal cell carcinomas do not stain positive for CD34 antigen on immunohistochemistry.

Trichodiscomas are clinically indistinguishable from fibrofolliculomas. It is particularly difficult when they present together in the Birt-Hogg-Dubé syndrome. Histologically, they appear similar as well. The only difference is that fibrofolliculomas have proliferation of cords of epithelial cells emanating from the hair follicle, but trichodiscomas do not have this feature. In fact, Ackerman et al. suggested that they are variations of the same lesion. Although they are still regarded as separate entities, keep in mind that there is some opinion towards unifying the two.

Trichodiscomas can also be confused with a lesion of colloid milium. This can be differentiated from trichodiscomas by histology. On histology, collioid milium consists of nodular fissured masses of amorphous eosinophilic material, located in the superficial dermis, with overlying epidermal atrophy and hyperkeratosis.

It is important to keep in mind that multiple firm dome-shaped papules on the head and neck are present in other syndromes as well (i.e. Brooke-Spiegler syndrome with multiple trichoepitheliomas); however, it is possible to differentiate Birt-Hogg-Dubé syndrome based on its specific systemic and other cutaneous findings compared to other syndromes.

Who is at Risk for Developing this Disease?

While the exact incidence is unknown, solitary trichodiscomas are rare benign tumors. They usually occur in the third or fourth decade and have a predilection for females. The exact incidence of both solitary and multiple trichodiscomas (Birt-Hogg-Dubé syndrome) is unknown. Other epidemiological details, including sex and age predilection, for solitary trichodiscomas are unknown.

Birt-Hogg-Dubé syndrome is more common in females, and onset is usually in the third or fourth decade. Patients also have a positive family history of the syndrome.

What is the Cause of the Disease?

Etiology

The etiology of solitary trichodiscoma remains unclear.

Pathophysiology

Solitary trichodiscomas are generally sporadic; however, mulitple trichodiscomas are associated with autosomal dominant Birt-Hogg-Dubé syndrome. Birt-Hogg-Dubé syndrome presents with multiple fibrofolliculomas, trichodiscomas, and acrochordons. Birt-Hogg-Dubé syndrome is associated with a gene defect in BHD gene (also known as FLCN gene), located on the 17p11.2 chromosome encoding folliculin protein product.

Systemic Implications and Complications

There are no systemic implications or complications associated with trichodiscomas, and no further management or patient work-up is warranted; however, patients with Birt-Hogg-Dubé syndrome require further work-up as detailed below.

The diagnosis of Birt-Hogg-Dubé syndrome should be suspected in a patient with a family history of this syndrome who is presenting with five or more facial and truncal papules. A skin biopsy of the lesions should be done to confirm fibrofolliculoma or trichodiscoma. If either one is diagnosed on biopsy, the patient should have further screening for renal and lung involvement, as this syndrome is associated with kidney tumors and bilateral and multiple lung cysts that result in an increased risk of spontaneous pneumothoraces.

The patient should have an abdominal computed tomography (CT) scan or renal ultrasound to look for renal tumors, as well as a chest CT or x-ray to confirm the diagnosis of bilateral lung cysts. After abdominal CT and/or renal ultrasound at the time of diagnosis, the patient should have subsequent screening every 3-5 years for renal tumors.

A spontaneous pneumothorax is more likely to occur in younger patients with Birt-Hogg-Dubé syndrome. Patients with this syndrome should be informed of the increased risk of pneumothorax and should be educated on the signs and symptoms of pneumothorax.

Genetic counseling and prenatal work-up should be offered to any individual who has a family history of this syndrome.

It is important to note that there are several other conditions associated with this syndrome. These include: medullary thyroid cancer, thyroid adenoma, parotid oncocytoma, multiple lipomas and angiolipomas, intestinal polyposis, neural tissue tumors, parathyroid adenomas, and large connective tissue nevus; however, most of these associations are based on anecdotal evidence and are based on a small number of case reports. On the other hand, there is strong evidence for renal and pulmonary associations; therefore, work-up should be geared towards these two organ systems primarily.

There are rare case reports of patients with Birt-Hogg-Dubé syndrome and their family members having an associated increased risk of melanoma. Routine screening with full cutaneous examination is recommended for these patients, and all suspicious pigmented lesions should be biopsied.

Treatment Options

Treatment options are summarized in Table I.

Table I.

Medical Treatment	Surgical Procedures	Physical Modalities
Topical	Shave removal	Laser Ablation
• Tretinoin	Punch excision	• Carbon dioxide laser alone
• Metronidazole	Excisional surgery	• Er:YAG (erbium:yttrium aluminum garnet) laser alone
Oral Isotretinoin	Electrosurgery	• Combination of carbon dioxide and Er:YAG laser

Optimal Therapeutic Approach for this Disease

Once the diagnosis of trichodiscoma is confirmed clinically and pathologically, treatment should focus on reassuring the patient about the benign nature of the lesion. If the patient has cosmetic concerns associated with the tumor, treatment can be initiated.

TREATMENT FOR SOLITARY TRICHODISCOMAS

Complete surgical excision is the best option for solitary trichodiscomas. Basal cell carcinoma is an important differential diagnosis that needs to ruled out. With surgical excision, tissue can be sent for pathology, and the deeper dermal component can be fully excised. If incompletely treated or excised, adnexal neoplasms like trichodiscomas can continue to grow and recur.

Deep shave of the lesion can be done, but it will not guarantee that the entire tumor is removed, and there will be a chance of recurrence. In addition, if the tumor is small, a punch excision around the visible tumor margins can be attempted. Although there is no guarantee, this method may reduce the chance of recurrence, and the defect size may be smaller than a complete surgical excision. Depending on patient’s budget, laser options can also be offered.

TREATMENT FOR MULTIPLE TRICHODISCOMAS ASSOCIATED WITH BIRT-HOGG-DUBÉ SYNDROME

The treatment options differ in the management of multiple trichodiscomas associated with Birt-Hogg-Dubé syndrome. It is important to realize that all of the surgical modalities can result in scarring; however, surgical excision is not a practical option for patients with Birt-Hogg-Dubé syndrome with multiple lesions. Therefore, medical treatment, mainly topical tretinoin and metronidazole, has been tried with improvement, according to one case report; however, the article did not report the specific strengths of tretinoin or metronidazole.

Patients should be informed that the goal of topical treatment is to reduce the size of the lesions, and that it will not result in eradicating the lesions.

Oral isotretinoin is not recommended, as it has been attempted in the past and there is no good evidence that it has been effective.

If medical remedies have failed or if the patient requires more aggressive approaches, surgical or physical modalities, such as electrosurgery or laser ablation, can be considered.

Laser modalities such as carbon dioxide laser and Er:YAG (erbium:yttrium aluminum garnet) laser alone or in combination can be used for multiple lesions. The combination of carbon dioxide and Er:YAG laser ablation has been reported with good result, with significant flattening of lesions and general smoothing of the skin. The Er:YAG laser ablates tissue with minimal thermal damage and allows debulking to an appropriate depth, thereby limiting the extent of scar formation. Because the Er:YAG is not hemostatic, the carbon dioxide laser is useful for additional carbonization and hemostatic effect.

Electrosurgery can also be used, but hypopigmented scars may replace the lesions because of thermal effects. A limited depth of treatment with electrosurgery also increases the risk of recurrence. Also, laser ablation is more precise and thus scarring is less likely.

Patient Management

It is important to inform patients that all treatment options can result in recurrence of the lesions.

In addition, in the case of Birt-Hogg-Dubé syndrome, new lesions may appear even if previous lesions have been treated successfully.

Unusual Clinical Scenarios to Consider in Patient Management

Multiple desmoplastic melanomas were reported in one patient with Birt-Hogg-Dubé syndrome. While the exact mechanism is not known, it is possible that Birt-Hogg-Dubé syndrome leads to expression of inactive folliculin, which can result in mTOR pathway activation.

Folliculin is thought to play a role in tumor suppression and have an inhibitory effect, particularly in the mTOR pathway. It is known that unregulated mTOR activation can result in cell growth and proliferation, as observed in melanoma pathogenesis. Therefore, it is advisable to perform routine full cutaneous examinations in these patients.

What is the Evidence?

Vincent, A, Farley, M, Chan, E, James, WD. “Birt-Hogg-Dubé syndrome: A review of the literature and the differential diagnosis of firm facial papules”. J Am Acad Dermatol. vol. 49. 2003. pp. 698-705. (This is a clinical review of Birt-Hogg-Dubé syndrome. This review details the diagnosis, differential diagnosis, and the skin tumors and systemic findings associated with the syndrome.)

Welsch, MJ, Krunic, A, Medenica, M. “Birt-Hogg-Dubé syndrome”. Int J Dermatol. vol. 44. 2005. pp. 668-73. (This is a good review about Birt-Hogg-Dubé syndrome that also discusses the history and treatment of the syndrome.)

Pinkus, H, Coskey, R, Burgess, G. “Trichodiscoma: a benign tumor related to haarscheibe (hair disk)”. J Invest Dermatol. vol. 63. 1974. pp. 212-8. (This is an article about trichodiscoma that discusses many details of its histology. It also explains the differential diagnosis of the tumor.)

Jacob, CI. “Birt-Hogg-Dubé syndrome: treatment of cutaneous manifestations with laser skin resurfacing”. Arch Dermatol. vol. 137. 2001. pp. 98-9. (A case report of combination of Er:YAG laser and carbon dioxide laser ablation and resurfacing treatment for a patient with Birt-Hogg-Dubé syndrome. It explains the post-operative outcomes and discusses the treatment protocol in detail:

First, laser skin resurfacing should be attempted with carbon dioxide laser at 300mJ/pulse, 60W, computer pattern generator handpiece pattern of 2, size 9, and a density of 5 for total of two passes. Then, individual lesions should be treated with a 3mm hand piece, settings of 500mJ per pulse, 3W, and for total of three to five passes until lesions are clinically flat.
Thereafter, each lesion should be treated with one pass of the Er:YAG laser at fluencies of 5.2J/cm2 (7mm handpiece, 2J) overlapping each spot by 50%.
Postoperative care should be performed.)

Gambichler, T, Wolter, M, Altmeyer, P, Hoffman, K. “Treatment of Birt-Hogg-Dubé syndrome with erbium:yag laser”. J Am Acad Dermatol. vol. 43. 2000. pp. 856-8. (This is a case report about treatment of Birt-Hogg-Dubé syndrome with erbium:Yag laser alone. It discusses the different treatment options and their advantages and disadvantages.)

Cocciolone, R, Crotty, K, Andrews, L, Haass, N, Moloney, F. “Multiple desmoplastic melanoma in Birt-Hogg-Dubé syndrome and a proposed signaling link between folliculin, the mTOR pathway, and melanoma susceptibilty”. Arch Dermatol. vol. 146. 2010. pp. 1316-8. (This is a case report of a rare association of melanoma with Birt-Hogg-Dubé syndrome. It also explains molecular pathways and their potential roles linking the two diseases. This report helps to modify the management of patients with Birt-Hogg-Dubé syndrome.)

Chartier, M, Reed, ML, Mandavilli, S, Fung, M, Grant-Kels, JM, Murphy, M. “CD34-reactive trichodiscoma”. J Cutan Pathol. vol. 31. 2004. pp. 398-400. (This is an article detailing the immunohistochemistry of trichodiscoma, and it also discusses the different staining pattern of CD34 in different diseases that clinically resemble trichodiscomas.)

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