Pink nodule on the toe of an infant

This The Clinical Advisor CME activity consists of 3 articles. To obtain credit, read Lesions with raised keratotic borders and Grouped pustules on a red base. Then take the post-test here.Infantile digital fibroma is also known as inclusion body fibromatosis.1...

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This The Clinical Advisor CME activity consists of 3 articles. To obtain credit, read Lesions with raised keratotic borders and Grouped pustules on a red base. Then take the post-test here.

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Infantile digital fibroma is also known as inclusion body fibromatosis.¹ It was first described by Reye et al. in 1965, who referred to the condition as a recurring digital fibrous tumor of childhood.² 


Infantile digital fibroma is a relatively rare condition with approximately 200 cases described in the literature.³ The condition has almost exclusively been reported in infants younger than age 1 year, with 47% of patients developing these lesions in the first month of life.⁴ 


In rare cases, infantile digital fibromas present later or earlier in life. There are 4 case reports of lesions resembling infantile digital fibroma developing in adults and also rare reports of congenital lesions presenting at birth.^4,5 These types of rare cases have been reported equally in males and females.


Clinically, infantile digital fibromas often present as firm, smooth, skin-colored nodules, although they may also appear more erythematous or pink.⁶ The most common location of these lesions is the dorsolateral aspect of the fingers and toes, typically on the distal aspects of the digits.^1,4 Infantile digital fibromas classically spare the thumbs or great toes.⁴ There have been no reports of metastases, but these lesions can infiltrate deeply.⁴ When infantile digital fibromas first appear, there is often a period of indolent progression, followed by a rapid growth phase during several months.⁷ 


The diagnosis is usually made clinically. However, if confirmation is required or desired, a skin biopsy is diagnostic. Infantile digital fibromas are comprised of dermal or subcutaneous proliferations of myofibroblasts.¹ The myofibroblasts are spindle-shaped, with uniform, wavy nuclei without nuclear atypia or mitoses.¹ The diagnostic feature of infantile digital fibromas is intracytoplasmic inclusion bodies that are composed of bundles of actin-like filaments.¹ Although these intracytoplasmic inclusion bodies are readily visible with hematoxylin and eosin (H&E) stains of specimens from skin biopsy, identification of these inclusion bodies can be facilitated with Masson trichrome or phosphotungstic acid hematoxylin (PTAH) staining.¹ The inclusion bodies stain red with Masson trichrome and purple with PTAH staining. The epidermis is typically spared.⁴ Although intracytoplasmic inclusion bodies comprised of actin filaments are thought to be pathognomonic for infantile digital fibroma, identical intracytoplasmic inclusion bodies have been reported in a benign phyllodes tumor of the breast in an adult female and a fibroadenoma of the breast in an adult male.^8,9 


The etiology of infantile digital fibroma is unknown.⁶ Viral etiologies have been proposed based on the associated intracytoplasmic inclusion bodies; however, no evidence supports this hypothesis at this time.⁶ 


Infantile digital fibromas have a very characteristic appearance so there is often no differential diagnosis. However, for smaller tumors, the differential diagnosis might include acral or acquired digital fibrokeratomas, periungual fibromas, or supernumerary digits.¹ Acquired digital fibrokeratomas have a distinct appearance in which the exophytic papule is usually surrounded by a collarette of scale at the base and are usually much smaller than infantile digital fibromas.¹ Moreover, acquired digital fibrokeratomas are seen almost exclusively in middle-aged adults.¹ Periungual fibromas are usually seen in association with tuberous sclerosis; however, isolated cases in otherwise healthy patients have been reported. Periungual fibromas that are associated with tuberous sclerosis typically develop from late childhood to adulthood, so by this age, the patient should already demonstrate other pathognomonic features of tuberous sclerosis. Acquired periungual fibromas may be related to acquired digital fibrokeratomas and thus, also seen later in adulthood unlike infantile digital fibromas, which are almost exclusively observed in infants. Supernumerary digits are small, pink papules, whereas infantile digital fibromas are usually much larger. Supernumerary digits are also characteristically bilateral lesions, located on the lateral aspects of the fifth fingers.¹ 


Other entities sometimes discussed in the differential diagnosis of infantile digital fibroma includes pachydermodactyly, keloids, and juvenile aponeurotic fibroma.¹⁰ Pachydermodactyly is a form of fibromatosis that is characterized by proximal thickening of the fingers and is seen more commonly in young adult males. As pachydermodactyly typically affects a much older subset of patients, it would be unusual to confuse this condition with infantile digital fibroma.¹⁰ With keloids, careful questioning to ascertain a history of preceding trauma, either accidental or iatrogenic (i.e., surgery), will help differentiate it from infantile digital fibroma. Juvenile aponeurotic fibromas are more commonly located on the palms and soles, whereas infantile digital fibromas are most commonly located on the distal aspects of the fingers or toes.¹⁰ 


In all instances, if the diagnosis is in question, a skin biopsy provides a definitive diagnosis.


Multiple infantile digital fibromas have been reported in association with a rare genodermatosis terminal osseous dysplasia with pigmentary defects.¹⁰ However, this entity is seen only in juvenile females and is almost always accompanied by facial and eye abnormalities, such as colobomas or hypertelorism.¹⁰ 


Infantile digital fibromas usually regress spontaneously within 2 to 3 years.¹ Surgical excision was recommended in the past, but high rates of recurrence have been observed. Because these lesions will spontaneously resolve and surgical excision often results in high rates of recurrence, observation is now recommended.


In severe cases, infantile digital fibromas can cause contractures or joint deformities, including lateral deviation of joints.^1,6 Therefore, if the lesion’s size or location results in functional impairment, such as contractures, surgical excision can be recommended with additional surgery as necessary for recurrences.¹ Mohs microscopic surgery has been reported as an effective surgical modality for infantile digital fibroma. Theoretically, rates of recurrence are lower with Mohs microscopic surgery as the margins are checked prior to closure; however, this has not been proven in larger studies.⁵ 


There are scattered case reports of alternative treatment modalities other than observation or surgical excision. Intralesional 5-fluorouracil and intralesional triamcinolone have been reported as effective in isolated cases, but since the natural history of infantile digital fibromas is that of spontaneous resolution, it is difficult to determine the additional benefit of these interventions.¹⁰ 


With our patient, a skin biopsy confirmed the diagnosis of infantile digital fibroma. The infant’s parents opted for observation, since the lesion was not causing any functional impairment. The lesion was stable in size at the 2-month follow-up visit. 


Audrey Chan, MD, is a pediatric dermatology fellow at Texas Children’s Hospital in Houston.


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This The Clinical Advisor CME activity consists of 3 articles. To obtain credit, read Lesions with raised keratotic borders and Grouped pustules on a red base. Then take the post-test here.

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This The Clinical Advisor CME activity consists of 3 articles. To obtain credit, read Lesions with raised keratotic borders and Grouped pustules on a red base. Then take the post-test here.

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