Inclusion body fibromatosis – A report of four cases and review of literatureMA Agnihotri, PA Sathe
Department of Pathology, Seth G. S. Medical College, Mumbai, Maharashtra, India
Keywords: Digits, fibromatosis, inclusions
Inclusion body fibromatosis or Infantile digital fibromatosis (IBF) is a rare fibroblastic proliferation of childhood with distinct clinicopathologic features. The prevalence is 2.5%. The lesion type is typically seen within first few years of life and may also be detected at birth. The classic location is the hands and feet. The detection of the characteristic paranuclear inclusions at microscopic assessment distinguishes it from other fibromatoses. With this report of four cases collected over a 12-year period, we wish to re-emphasize the typical features of this rare entity.
A three-year-old female child presented with non-tender, firm swellings on the dorsal surface of right first, second and fifth finger of six months duration. The swellings measured 1.5 × 1 × 0.3 cm, 0.2 × 0.1 cm and 1.5 × 1.2 × 0.3 cm, respectively. There was a history of a similar swelling on the right third finger two years previously.
A two and a half-year-old male child presented with a gradually increasing single non-tender firm nodule measuring 2 × 1 cm in size over the dorsal aspect of his right fifth toe since the sixth month of life. Clinically, the skin over the nodule appeared stretched and tense and had there was restricted mobility of the fifth toe.
A three-year-old male child presented with a non-tender firm swelling measuring 1 × 1 × 0.5 cm on the lateral aspect of the right fourth toe of two years duration [Figure 1]a. The patient's parent gave a history of similar swelling on the right fifth toe diagnosed one year previously for which intra lesional triamcinolone was injected.
A one-year-old female child presented with swelling over the right fifth toe of size 1.4 × 0.7 cm since five months. There were no other complaints.
None of the cases had a history of trauma (neither microtrauma nor with hematoma). Out of the eight swellings, seven were excised (except the one for which intra lesional triamcinolone was injected) .Grossly, the lesions were skin-covered nodular lesions and were gray-white and firm on cut surface [Figure 1]b. The overlying skin was stretched and not ulcerated. The entire lesion was analyzed on microscopy.
All lesions showed similar microscopy aspects. The microscopic assessment showed a non-encapsulated tumor composed of fascicles of uniform spindle cells resembling fibroblasts/myofibroblasts with deposition of extracellular collagen. The overlying skin showed acanthosis for two lesions and atrophy for five lesions. The spindle cells surrounded the dermal appendages. The characteristic intracytoplasmic paranuclear inclusions were detected in all nodules. Special stains highlighted the inclusions red on Masson trichrome stain and purple on Phosphotungstic acid hematoxylin (PTAH) stain [Figure 1]c,[Figure 1]d,[Figure 1]e,[Figure 1]f. A diagnosis of inclusion body fibromatosis was made for all tumors. None of the cases had recurrence of lesions on follow up ranging from six months to eleven years.
The solitary lesion of IBF typically occurs on the dorsal or lateral aspects of the digits, sparing the thumb and the great toe. Synchronous or metachronous occurrence of multiple lesions has been reported., Out of the two cases of the present series who had multiple lesions, one case had synchronous and metachronous leisons while the second case had metachronous lesions. The maximum number of nodules seen per case in the present series was four. Other rare extra-digital sites of IBF are soft tissues of the arm, breast, tongue and thigh. The lesions of IBF are smooth and dome-shaped, with the overlying skin being flesh-colored to red and are usually asymptomatic. The size of the lesions rarely exceeds 2 cm as also seen in the cases of the present series. Larger tumors may cause pain, hindrance in activities or long-term functional consequences. IBF is typically seen in the first three years of life but can occur also at birth. However, some authors have reported cases upto 10 years and even later. There is no gender predilection as observed in the present series as well. The clinical diagnosis is usually that of a keloid or a hypertrophic scar. Microscopically, the lesions typically show intradermal proliferation of fibroblasts/myofibroblastic spindle cells arranged in fascicles perpendicular to the epidermis. The cells are bland and show mitotic figures only rarely. The hallmark feature is the presence of inclusions. All cases in our series had classic features in terms of location, age of the patient (<three years), size of the lesion (<2 cm), bland histology and the characteristic inclusions.
Immunohistochemical demonstration of actin filaments by smooth muscle actin, desmin, and calponin may be required for diagnosis. Immunohistochemistry was attempted in one case of the present series but it did not yield conclusive results. In few cases, the inclusions may be absent. This may be attributed to the age of the lesion. Younger lesions have more inclusions and less fibrosis as compared to older lesions. Fine-needle aspiration cytology is also an effective tool for diagnosis of this tumor type. The inclusions can also be detected on cytology smears provided there is high index of suspicion and awareness about IBF. Histologically, these lesions need to be differentiated from other fibromatoses occurring in this age group. Paranuclear inclusion is the diagnostic feature of this entity. However, in its absence, typical location, size, age group, absence of mitoses, and absence of nuclear atypia can be used as diagnostic criteria. IBF have a tendency for spontaneous regression and hence conservative management is preferred. The etiology and pathogenesis of this entity is not clear. There is no known association with any genetic disorder or malformation. Currently, the inclusions are believed to be the result of deviation in the complex process of myofilament assemblage in myofibroblasts and smooth muscle cells. Surgery is indicated only in cases with functional impairment. Intra-lesional steroids and chemotherapeutic agents have been tried in some cases as also seen in one lesion of the present series. Though the lesions have a high recurrence rate, overall, the prognosis is excellent.
Approximately 200 cases of IBF have been reported in medical literature so far. The largest series has been reported by Laskin et al. comprising 74 lesions from 57 patients. Few other case series have been reported which had more than eight nodules. Thus, our series comprising eight nodules from four patients is one of the largest series of cases of IBF reported in medical literature.
Inclusion body fibromatosis is a rare benign myofibroblastic proliferation of childhood occurring typically on the digits and toes with characteristic inclusions. Awareness about this entity and diligent search for inclusions is essential for accurate diagnosis.
Declaration of patient consent
The authors certify that appropriate patient consent was obtained.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.