Tuesday 13 June 2006
Definition: Collagenomas (connective tissue nevi of collagen type) are rare hamartomas of the skin in which there is an increase in dermal collagen.
Collagenomas usually present as asymptomatic, firm, flesh-colored plaques and nodules, 0.5–5.0 cm in diameter, on the trunk and upper part of the arms. The ear, sole of the foot, and vulva are rare sites of involvement.
There may be several lesions or up to a hundred or more, with an onset in adolescence.
Eruptive collagenomas have also been reported as the only lesion.
Uncommonly, they occur in a zosteriform or linear distribution.
Rapidly growing (eruptive) collagenomas have been reported in the multiple endocrine neoplasia type I syndrome, and in pregnancy.
A family history is sometimes present (familial cutaneous collagenoma) and in these cases there is autosomal dominant inheritance. Familial cutaneous collagenomas (MIM.115250) result from a mutation in the LEMD3 gene, as seen in the Buschke–Ollendorff syndrome.
Associated clinical features include a cardiomyopathy, Down syndrome, and occult spinal dysraphism.
Uncommonly, the connective tissue nevi associated with the Buschke–Ollendorff syndrome are of collagenous composition rather than of the usual elastic tissue type.
A connective tissue nevus of collagen type has been reported in association with pseudo-Hurler polydystrophy (mucolipidosis III), and in Proteus syndrome, in which the nevi are often acral, sometimes of the plantar cerebriform type.
Plantar collagenomas can occur in the absence of the Proteus syndrome.
Solitary collagenomas are sometimes quite large, as seen with the cerebriform or ‘paving stone’ variants on the sole of the foot.
Cutis verticis gyrata
Sometimes a connective tissue nevus is associated with cutis verticis gyrata, a descriptive term for a condition of the scalp in which deep furrows and convolutions are present. The folds of skin may, however, have normal morphology.
Other pathological associations of cutis verticis gyrata include lymphedema, mental retardation, adipocyte proliferation, acromegaly, misuse of anabolic substances, myxedema, Noonan syndrome, tumors, and the insulin resistance syndrome.
Cutis gyrata, usually on the scalp, can be seen in the Beare–Stevenson syndrome (MIM.123790) characterized by mutations in the transmembrane region of fibroblast growth factor receptor-2 (FGFR2) located at chromosome 10q26. Acanthosis nigricans, skin tags, and anogenital anomalies are other features of this syndrome.
There is a reduction in expression of tuberin in connective tissue nevi associated with the tuberous sclerosis complex.
The epidermis is usually normal, although an overlying epidermal nevus has been reported.
There is thickening of the dermis, sometimes with partial replacement of the subcutis. The collagen bundles are broad and have a haphazard arrangement. Elastic fibers are more widely spaced, but this may represent a dilution phenomenon.
Sometimes the elastic fibers are thin and fragmented. Some of these cases may represent papular elastorrhexis. There is no increase in mucopolysaccharides.
Dermal dendrocytes are reduced using antibodies against factor XIIIa. Calcification was present in one reported case.
As the collagen in collagenomas is less well packed than normal, differences in polarization colors can be seen with picrosirius red staining followed by polarization microscopy. The fibers appear green to yellow, in contrast to the orange to red color of normal dermal collagen.
Collagenomas must be distinguished from sclerotic fibromas which present as tumor-like nodules. They have a characteristic histological appearance with dense collagen bundles, often in a storiform arrangement.
Athlete’s nodules are related to, but different from, collagenomas. One such example is the dermal nodule found in the sacrococcygeal region of bicycle riders.