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.
Birt-Hogg-Dubé syndrome presents with multiple fibrofolliculomas, trichodiscomas, and acrochordons. On physical exam, both fibrofolliculomas and trichodiscomas are indistinguishable, presenting as small dome shaped papules. Acrochordons are usually soft and pedunculated.
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.
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?
The etiology of solitary trichodiscoma remains unclear.
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 are summarized in
Treatment options for trichodiscoma.
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.
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.
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.
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.)