Eruptive collagenoma: A rare connective tissue hamartoma presenting with an unusual morphology

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Collagenoma is a connective tissue nevus predominantly composed of collagen.¹ Collagenomas represent benign hamartomatous lesions of the dermis of unknown aetiology. They are classified as inherited or acquired; inherited include familial cutaneous collagenomas and shagreen patches of tuberous sclerosis and the acquired include eruptive collagenomas and isolated collagenomas.² We report here an unusual case of eruptive collagenoma in a middle-aged man.

A 51-year-old man presented to us with gradually progressive, asymptomatic symmetric eruption of multiple, skin-coloured, raised lesions present on chest, abdomen, upper back and bilateral arms for seven months. There was no past history of trauma or skin eruptions at the site of lesions. Systemic examination showed no abnormality. On dermatological examination, multiple partly circumscribed, discrete to coalescent, firm, waxy flesh-coloured to dusky red nodules and plaques of varying sizes, 0.5 × 0.5 cm² to 2.0 × 2.0 cm² were present symmetrically on chest, upper back (scapular region) and proximal upper limbs [Figures 1a and 1b]. The overlying skin showed no surface changes; mild tenderness was present over larger coalescent lesions. The mucosae, scalp and nails were normal.

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Figure 1a:

Multiple, well-defined nodules coalescing to form plaques present symmetrically on upper chest, proximal limbs and abdomen

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Figure 1b:

Multiple well- to ill-defined, discrete to coalescent, firm, waxy flesh-coloured to dusky red nodulo-plaques varying from 0.5 × 0.5 cm² to 2.0 × 2.0 cm² in size present symmetrically on upper back (scapular region) and proximal upper limbs

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Differential diagnoses of mycosis fungoides, primary cutaneous B-cell lymphoma, amyloidosis, leiomyomas, multiple keloids, papular mucinosis/lichen myxedematosus and histoid leprosy were considered. A skin biopsy was done and on histopathological examination mild acanthosis of epidermis, dense collagenization in the reticular dermis with a mild perivascular infiltrate of lymphocytes and plasma cells were observed [Figure 2a]. Zeihl neelsen and Alcian Blue stain were negative for acid fast bacilli and mucin deposition. Masson’s trichrome and Verhoeff-van-Gieson stains showed markedly increased collagen arranged in a haphazard pattern in the dermis with a reduction in elastin fibres [Figure 2b]. With clinical and the histopathology findings, two differential diagnoses were considered, familial cutaneous collagenoma and eruptive collagenoma.

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Figure 2a:

(Low power, 10× lens total magnification 100×) Mild acanthosis, reticular dermis shows dense collagenization, scantly infiltrate

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Figure 2b:

(Masson’s Trichrome, 400×) Dense collagen fibres throughout dermis

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Eruptive collagenoma was first described by Colomb in 1955.³ They usually present in the first two decades of life and lesions tend to be asymptomatic, cutaneous nodules which are distributed symmetrically on head and neck, upper and lower limbs.⁴ Histologically, it is characterised by dense coarse collagen fibres arranged haphazardly in dermis with a decrease in elastic fibres.⁵ Eruptive collagenoma needs to be differentiated from familial cutaneous collagenoma which is inherited in an autosomal dominant pattern with a positive family history.⁶ Familial cutaneous collagenoma (FCC) may be associated with cardiac abnormalities such as progressive cardiomyopathy and conduction defects attributed to fibrotic process affecting various structures of the heart.⁷ Lesions of FCC usually affect the trunk (upper back) and tend to be more numerous than the lesions of eruptive collagenoma which mainly affect the periphery including head, neck, upper and lower limbs.⁴ In our case, there was no family history and there was no evidence of any cardiovascular disease. Based on these findings, we diagnosed this as a case of eruptive collagenoma. A review of literature of similar cases has been presented in Table 1. We report this case of eruptive collagenoma due to its unusual distribution and morphology where histopathology helped us clinch the diagnosis.