Oral focal mucinosis of the mandible in an adolescent patient

Abstract

Oral focal mucinosis (OFM) is the rare oral manifestation of cutaneous focal mucinosis. It is a diagnosis made histopathologically, as OFM remains clinically similar to other more common oral lesions, and radiographs do not provide any diagnostic information. This case is a report of a teenage female with left mandibular involvement of an elevated, rounded, asymptomatic, mucosa-coloured lesion in the facial and lingual gingiva between her left first and second mandibular molars. The cause was unclear, although the patient stated that she may have sustained a laceration in that area several months prior. An incisional biopsy revealed histopathological findings consistent with OFM, and complete surgical excision of the lesion was performed under a general anaesthetic, with no signs of recurrence for 2 months. The histological, clinical and accepted treatment methods on OFM will be discussed. Clinicians, including those serving paediatric populations, should consider OFM in their differential diagnoses when evaluating gingival lesions.

Background

The exact aetiology of oral focal mucinosis (OFM) remains unknown, but the lesion is thought to result from increased production of hyaluronic acid by fibroblasts, which subsequently creates localised proliferation of loose, myxoid fibrocollagenous tissue. It is the rare oral manifestation of the more common cutaneous focal mucinosis. Tomich in 1974 presented the first description of an oral lesion, with subsequent case series and reports describing lesions with similar clinical features: asymptomatic, pedunculated or sessile, with a predilection for keratinised tissue such as gingiva or hard palate.^1–3

OFM occurs mainly in adults in the fourth to fifth decade of life, although there have been few case reports in a child as young as 2 years of age.^{2 3} There is a distinct ratio favouring females to males, with an approximate ratio of 3:1, with the gingival origin being the most common, followed by in the hard palate, buccal mucosa, tongue, retromolar region and lip.^{1 4–7}

Case presentation

Our patient is a 13-year-old female who presented regularly to the local children’s hospital paediatric dental clinic for routine dental care. The lesion, a focus of hyperplastic gingiva in the buccal gingiva of the mandibular left first and second molars was noted in October 2018 in the paediatric dental clinic as being present for a few weeks and thought originally to be reactive soft tissue from a healing intraoral laceration. As it did not resolve, she was referred in February 2019 to the Oral and Maxillofacial Surgery Department at University of Pittsburgh Medical Center. Her medical history was significant for anxiety, attention deficit hyperactivity disorder and global developmental delay, but otherwise unremarkable. Her family history reported no oral lesions or tumours.

Investigations

Clinically, the patient appeared healthy, in no discomfort, and with no obvious extraoral swelling. Intraoral examination revealed pink, sessile, hyperplastic multilobulated tissue masses without ulceration on both facial and lingual aspects of her gingiva between the mandibular left first and second molars. The facial mass and lingual mass were both approximately 1.5 cm in the widest dimension. The masses were firm in consistency with no fluctuance. The associated teeth were not tender to palpation and not mobile. Her occlusion was otherwise stable and reproducible. A panoramic radiograph showed no osseous lesions around the teeth, with intact lamina dura noted around all roots (figure 1).

Figure 1.

Diagnosis and excision of lesion. (A) Orthopantomogram. (B) Intraoral buccal view. (C) Intraoral occlusal view. (D) Excisional biopsy buccal. (E) Excisional biopsy lingual. (F) Periodontal dressing.

Differential diagnosis

The clinical differential diagnosis typically includes fibroma, peripheral ossifying fibroma, peripheral giant cell granuloma, peripheral odontogenic fibroma and pyogenic granuloma. However, pyogenic granulomas and peripheral giant cell granulomas often tend to be ulcerated. Less likely diagnoses include fibrous hyperplasia, which often has a genetic basis and is usually bilateral, and peripheral ameloblastoma, which is also unlikely due to her young age.^{8 9}

Treatment

The patient initially underwent an incisional biopsy under general anaesthesia in April 2019 of both facial and lingual masses, which were placed in 10% formalin and sent to the oral pathologist. The biopsy revealed a well-localised, unencapsulated area of loose, myxomatous connective tissue with short bands of delicate collagen. Stellate and spindle-shaped fibroblasts are scattered throughout the mucinous area. An S-100 immunohistochemical stain was performed to evaluate for a myxoid lesion of neural origin. The stain highlighted a few scattered melanocytes and dendritic cells, mostly confined to the epidermis, but not in the mucinous areas (figure 2).

Figure 2.

Representative sections of the incisional biopsy demonstrating a diffuse, myxoid stroma with numerous stellate-shaped fibroblasts. (A) H&E (20×). B. An S-100 immunohistochemical stain highlights scant, scattered dendritic cells, mostly confined within the epithelium.

The patient returned for an excisional biopsy in June 2019 to remove all lesion tissue in its entirety. A periodontal dressing packing material was placed (COE-PAK) over the surgical site. The biopsy was also sent to the oral pathology department, where the final diagnosis of oral focal mucinosis was confirmed.

Outcome and follow-up

She returned for a follow-up visit approximately 3 weeks later, where she was asymptomatic and had adequate granulation of her surgical site. She later returned for her 8-week follow-up, where she remains well and soft tissue had fully grown into her surgical site (figure 3).

Figure 3.

Intraoral postop-photos. (A) 3-week buccal view. (B) 3-week occlusal view. (C) 8-week buccal view. (D) 8-week occlusal view.

Discussion

This case report depicts the lesion of OFM on the left mandible gingiva of an adolescent patient. The aetiology of this lesion is unclear, though a study by Neto et al suggested trauma could be the predisposing factor.⁵ Previous studies have mentioned overproduction of hyaluronic acid by surrounding fibroblasts in the stroma, which intrudes into the surrounding collagen.^{1–4 10} There have been several reported cases of OFM in the adolescent and paediatric populations, as young as 2 years of age. Most case reports describe a single lesion, though Yadav et al reported a bi-maxillary case in 2016.⁵ Overall, this is a relatively rare lesion, with about 68 reported cases since Tomich originally reported his case series in 1974.¹

The clinical diagnosis of OFM is impossible to make, as it appears indistinguishable from several other oral lesions of various etiologies, namely fibromas, pyogenic granulomas, peripheral giant cell granulomas, peripheral odontogenic fibromas and other benign tumours. The findings are usually of a painless elevated mass of firm consistency, with a colour similar to that of the surrounding tissue. Most cases are discovered during routine oral examinations, as these lesions are asymptomatic.^{1 10 11}

Radiographic findings are rare, though Higuchi et al mentioned an intraosseous retromolar growth that was originally thought to be an odontogenic myxoma, but histopathology subsequently revealed it to be OFM.⁴ Gabay et al reported a case of concurrent external cervical root resorption with OFM.¹² Diagnosis is made solely on histopathological findings.

Histopathological findings of OFM usually reveal stratified squamous mucosal epithelium with an underlying loose, myxoid, connective tissue stroma containing stellate-shaped fibroblasts adjacent to some normal collagen.⁸ The pathological differential diagnosis includes other lesions with highly myxomatous stromas, including peripheral odontogenic myxoma, mucocele and myxoid neurofibroma. Peripheral odontogenic myxomas are extremely rare, with only about three cases on the gingiva reported in the literature. Odontogenic rests of epithelium should be present in those specimens.¹³ Mucoceles, a lesion characterised by the traumatic extravasation of mucin from the minor salivary glands, should include macrophages filled with mucin, and most commonly a cavity filled with mucin, not interspersed among collagen bundles. Also, as this is the gingiva, there should be no salivary tissue. Lastly, the myxoid variant of a neurofibroma can also be considered in the pathological differential diagnosis. These lesions in the oral cavity are quite rare in the absence of syndromic neurofibromatosis. These lesions should stain strongly and diffusely with S-100.¹³ Specific histochemical stains can be used to highlight mucinous content if deemed necessary. Alcian blue will stain acidic mucous, such as the hyaluronic acid seen in OFM. A Periodic acid Schiff histochemical stain will highlight mucopolysaccharides, which are not present in OFM lesions.^{4 12}

The treatment of choice in this patient was complete surgical excision of her soft tissue lesion, which is the accepted method for OFM in previously noted case reports.^{5 6 8} There are rare reports of recurrence, with one recurrence noted due to incomplete excision.¹⁴ This patient will continue to be monitored and appears to be healing uneventfully with no signs of recurrence. Although rare, clinicians should consider OFM in their differential diagnoses for intraoral soft tissue lesions in adolescents and adults.

Learning points.

• Soft tissue lesions often appear clinically similar. Even with a clear and accurate history of the lesion that may point at one specific diagnosis, we highly recommend phasing treatment. An initial incisional biopsy for histochemical evaluation for final diagnosis, which then can guide the extent of a subsequent definitive surgery, which may or may not require a general anaesthetic, which comes with risks of its own.

• Although more common in the adult population, oral focal mucinosis (OFM) should be considered when evaluating paediatric soft tissue lesions as well.

• Overall, this case report reveals that while OFM is a rare lesion, clinicians should keep OFM on their list of differential diagnoses when evaluating soft tissue lesions in the mouth.