Differential Diagnosis Amputation neuroma secondary to supernumerary digit and Acquired digital fibrokeratoma

Amputation neuroma secondary to supernumerary digit Acquired digital fibrokeratoma 1. Increased number of large nerve trunks throughout a section of tissue 1. No nerve structures in the lesion itself 2. Nerve trunks and collagen bundles oriented perpendicular to the surface of the skin (i.e., parallel to the long axis of the anomaly elongate) 2. Collagen bundles arranged haphazardly 3. Fibrocytes normal cytologically not usually increased in number 3. Fibrocytes often large, stellate, or multinucleate are markedly increased in number 4. Collagen bundles thick and coarse 4. Collagen bundles mostly fibrillar; some are coarse

Discussion

Features clinical common to amputation neuroma secondary to rudimentary supernumerary digit and acquired digital fibrokeratoma are location, shape, and consistency. Both conditions occur on or near fingers and both are firm, keratotic, polypoid projections. Amputation neuromas are composed mostly of neural tissue; acquired digital fibrokeratomas are formed predominantly of fibrous tissue. In both abnormalities, widely dilated blood vessels tend to be present in the uppermost portion of the dermis.

Amputation neuromas secondary to supernumerary digits are stubs present at birth that represent neural remnants in skin of supernumerary digits lost, presumably, in utero. Amputation neuromas often occur in pairs at lateral aspects of fifth fingers. They are comparable to those neuromas that develop later in life at sites of surgical amputation, but can be differentiated from them histopathologically by polypoid shape and a cornified layer characteristic of volar skin.

A supernumerary digit, by contrast, is not a neuroma but a miniature digit constituted of bone, cartilage, muscle, and other components expected, such as nail plate, of a normal finger.

Unlike amputation neuroma and supernumerary digit, acquired digital fibrokeratoma is a solitary excrescence that arises from the skin of an adult near an interphalangeal joint of a finger. The projection may be elongated (polypoid) or domed (sessile), but always is keratotic. Other fibromas that have attributes histopathologic reminiscent of those in acquired digital fibrokeratomas are pearly penile papules. The denominators in common of these angiofibromas are marked vascularity and fibroplasia, the latter consisting mostly of fibrillar bundles of collagen and an increased number of large, stellate, and often multinucleate fibrocytes. Such fibrocytes tend to be found at sites of active, sustained manufacture of collagen bundles. Acquired digital fibroma, fundamentally, is a fibroma indistinguishable morphologically from the periungual and subungual fibromas of tuberous sclerosis.

An interesting parallel exists between fibrous papules of the face and acquired digital fibrokeratomas on the one hand, and the cutaneous fibromas of tuberous sclerosis on the other. Fibrous papules of the face are identical to papules of adenoma sebaceum in tuberous sclerosis, they being hamartomas that, in addition to angiofibromatous findings exhibit signs indisputable of follicular differentiation and, as has just been mentioned, acquired digital fibrokeratomas are indistinguishable from subungual and periungual fibromas that develop in children with tuberous sclerosis. Also noteworthy is the observation that the striking fibrocytes in cutaneous angiofibromas of tuberous sclerosis resemble closely glial cells in intracranial tubers of that phakomatosis. Perifollicular fibroma is a synonym for fibrous papule.

In sum, amputation neuroma secondary to loss in utero of a supernumerary digit and acquired digital fibrokeratoma look alike clinically and have a silhouette similar histopathologically. The former, however, is basically a neuroma, whereas the latter is a fibroma.

Ref:

Differential Diagnosis In Dermatopathology I, Ii, Iii, Iv.chm