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Abstract
Collagenomas are connective tissue nevi characterized by an imbalance in the distribution and amount of collagen in the extracellular matrix. Shagreen patch, a collagenoma of tuberous sclerosis, is a classical finding in this genodermatosis (Tuberous Sclerosis). Though the prototypical lesion is a shagreen patch, some individuals manifest only small collagenomas, and these can hinder a diagnosis of tuberous sclerosis and thus mask underlying systemic involvement as was seen in this case we have reported, wherein a 22-year-old male presented with segmental collagenomas over the face and calcified subependymal nodules of the brain on further investigation.
Keywords: Central nervous system involvement, collagenoma, tuberous sclerosis
Introduction 
Collagenomas, a type of connective tissue nevi, can be either inherited or acquired.[1] There are two entities which fall under the inherited type: familial cutaneous collagenomas and collagenomas associated with tuberous sclerosis complex (TSC). TSC is a neurocutaneous syndrome characterized by benign tumors of the skin, brain, lungs, heart, and kidneys.[2] The most important collagenoma associated with TSC is the Shagreen patch, which typically occurs over the lumbosacral area but can also present as small collagenomas elsewhere on the body. Here, we report a case with collagenomas occurring in a segmental fashion on the face, as a sole cutaneous indicator of tuberous sclerosis, which on further systemic examination revealed multiple, calcified subependymal nodules of the brain.
Case Report A 22-year-old male presented to the dermatology out-patient department with asymptomatic raised pigmented lesions over the left side of the face and nasolabial fold since birth. Though they were few in number at birth, as he attained puberty, these lesions began to increase in size and number. The patient had no similar lesions elsewhere in the body. There was no history of seizures, blurring of vision, headaches, renal, or cardiac diseases.
On examination, a solitary, ill-defined, pigmented plaque measuring 4 × 3 cm with an irregular surface was present on the left malar area extending to the left temporal area along with multiple, discrete pigmented papules on the left cheek [Figure 1]. There was no evidence of ulceration or bleeding. Clinically, we made a diagnosis of angiofibroma with connective tissue nevi and a skin biopsy was done from both lesions to confirm the diagnosis. On histopathological examination, sections from both specimens showed normal looking epidermis with collagen proliferation throughout the dermis, replacing the subcutaneous fat [Figure 2] with perifollicular fibrosis and atrophy [Figure 3], more indicative of a collagenoma. Immunohistochemistry with CD34 and Desmin was done to look for blood vessel proliferation and smooth muscle, respectively, and both were found to be negative. [Figure 4]a and [Figure 4]b Special stains with Masson's trichrome stained the slide blue [Figure 4]c, confirming the collagen proliferation and a diagnosis of collagenoma. The absence of elastic fibers was indicated by a lack of black staining on Masson's trichrome staining.
Figure 1: Clinical image showing a solitary, ill-defined, pigmented plaque measuring 4 × 3 cm with an irregular surface over the left malar area extending to the left temporal area along with multiple, discrete pigmented papules on the left cheek
Figure 2: Histopathological image in scanner view (10×) showing coarse hyalinized collagen deposition throughout the dermis replacing the subcutaneous fat as well
Figure 3: Histopathological image in high power view (40×) showing perifollicular fibrosis with atrophy
Figure 4: (a and b) Section showing negativity for Desmin and CD34, respectively, (c) Section showing a light blue color on Masson's trichrome staining, indicative of collagen. The absence pf black staining shows the negative staining for elastic fibersA computed tomography scan of the brain showed multiple calcified subependymal nodules and a small calcification in the right fronto-parietal region. Other investigations, like an ultrasound of the abdomen and an electrocardiogram, were normal.
Based on the above-mentioned findings, we made a possible diagnosis of tuberous sclerosis as more than two major criteria were fulfilled.
Discussion Connective tissue nevi, to which the collagenomas belong, are hamartomas, consisting predominantly of elements of the extracellular matrix like collagen, elastin, and glycosaminoglycans.[3]
Shagreen patch, i.e. a collagenoma of TSC, is considered a highly diagnostic feature of TSC and classically presents as a solitary, large, irregular, firm plaque with dilated follicular openings, giving it a “peau d'orange” or “pigskin” appearance. These are commonly seen over the lumbosacral region, but can occasionally be found elsewhere in the body.[4]
Histopathological examination of the collagenoma will reveal a dermis with relatively acellular, hyalinized collagen extending all the way to the subcutaneous fat, perifollicular fibrosis with atrophy and follicular compression, as well as thin, fragmented to almost absent elastic fibers.[5]
Tuberous Sclerosis is an autosomal dominant disease which occurs as a result of mutations in TSC 1 and TSC 2, located on chromosomes 9q34 and 16p13, respectively. The systemic spectrum of this disease was initially described as Vogt's triad, consisting of epilepsy, mental retardation (low intelligence quotient) and adenoma sebaceum (EPILOA), but this may not be consistently present in all cases. While the cutaneous manifestations of TSC include angiofibromas, fibrous plaque of forehead (fibrous cephalic plaques), hypomelanotic macules, shagreen patches and periungual tumors, systemic involvement commonly involves the central nervous system (CNS) and ophthalmic systemic with manifestations like mental retardation, persistent seizures, subependymal nodules, subependymal giant cell astrocytomas, cortical tubers, intracranial periventricular calcifications, and retinal phakomas to name a few.[6]
A study by G Raghu Rama Rao et al.,[6] discovered a link between fibrous forehead plaque and CNS involvement, demonstrating that a single cutaneous manifestation, such as a collagenoma, can conceal a much larger picture, such as calcified subependymal nodules, as seen in our case.
Conclusion Collagenomas present elsewhere in the body, i.e., other than the lumbosacral region can mimic collagenomas present in other conditions, thus hindering a diagnosis of tuberous sclerosis. This in turn can delay the identification of the various systemic manifestations of this genodermatosis. This case has thus been reported to highlight that such a presentation of cutaneous collagenomas occurring alone can turn out to be sinister, hence, it is imperative to be thorough in investigating and ruling out any hidden systemic involvement.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
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Conflicts of interest
There are no conflicts of interest.
References 
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