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Multiple eruptive dermatofibromas, a rare presentation of dermatofibroma, has been associated with altered immunity such as HIV/AIDS.

A 57-year-old man with a long history of HIV on antiretroviral therapy was referred to the dermatologic clinic from the Infectious Disease Service for evaluation of multiple hyperpigmented lesions appearing on extremities for the past year. The patient mentioned being under high stress in the previous year, which is when he first noticed the presence of macules. He reported that lesions were mostly pruritic with occasional tenderness, especially on areas of high abrasion. Some lesions also felt like bug bites and the number of lesions were increasing.

Prior to the visit, patient tested positive for Group A Streptococcus and received IM penicillin treatment. Laboratory investigations were notable for low WBC count of 3.7 (3.9 – 12.0 K/UL) and low absolute CD3/CD4 count of 360 (438 - 1,502 CEL/UL). Quantitative PCR for HIV Viral load detected low number of viral copies (around 30 copies/mL) which has remained stable since 2021, indicating the patient is adherent to his HIV treatment protocol.

The patient’s active medications include abacavir-dolutegravir-lamivudine (TRIUMEQ) 600-50-300 mg tablet daily, alprazolam 0.5 mg tablet as needed, amlodipine-olmesartan (AZOR) 5-20 mg tablet daily, Armour Thyroid 60 mg tablet, pregabalin 50 mg capsule daily, sertraline 100 mg tablet daily, tamsulosin 0.4 mg capsule daily, pravastatin 20 mg tablet daily, and mirabegron ER 50 mg tablet daily.

A physical exam showed numerous 5 mm to1 cm round hyperpigmented macules, dome-shaped papules, and nodules scattered on the left upper extremity and bilateral lower extremities with dimpling in some of the lesions. Skin biopsy was performed on medial posterior calf for immunohistochemical analysis.

Diagnosis

Eruptive Myxoid Dermatofibroma (superficial/cutaneous benign fibrous histiocytomas).

Microscopic Findings

Skin biopsy revealed myxoid dermatofibroma, an extremely rare variant of dermatofibroma, characterized by marked stromal mucin deposition. Immunohistochemical studies for CD 117 showed increased perivascular and stromal solitary mast cells. Colloidal iron stain confirmed mucin deposition on the stain.

Discussion

Dermatofibromas are commonly found benign nodular cutaneous lesions in the dermis or subcutis.¹ Dermatofibromas are also known by several names, including benign fibrous histiocytomas, superficial fibrous histiocytomas, cutaneous fibrous histiocytomas, common fibrous histiocytomas, or fibrous xanthoma in some contexts.² As the name “benign fibrous histiocytoma” suggests, there is a fibroblastic process of repair process and a mix of histiocytes, phagocytic cells derived from myeloid or Langerhans cell lineages, are usually seen in histology.³ The etiology is unknown, though often related to some injury or trauma to the skin when referring to cutaneous types such as a wound, injection, or insect bite.⁴ Clinically these lesions are seen more commonly on extremities of young to middle-aged females (20 to 40 years of age) though it may be found elsewhere on the body. The lesions are asymptomatic and occasionally pruritic.⁵ They are usually less than 10 cm, can be solitary or found in groups, are dark red or brown in color and create a central dimple when compressed.⁶

Pictured: Hyperpigmented macules and nodules on patient’s lower extremities

Histologically, dermatofibromas consist of fibroblasts and histiocytes and may be subclassified this way. There is debate as to whether these lesions occur with neoplastic or inflammatory process.⁵ Dermatofibroma presents with proliferation of histiocytic and spindle cells in a storiform pattern with collagen globules or “collagen balls” on the periphery.^6,7 In the case of our patient, myxoid type dermatofibroma, a very rare type of dermatofibroma, is characterized by marked stromal mucin deposition and found in 0.4% of all dermatofibromas.²

Dermatofibroma lesions generally present as solitary nodules, and when a patient presents with multiple eruptive lesions (MEDF) consisting of more than five nodules appearing in a short time frame of four months or less, one should strongly consider the patient may either have an underlying disease condition causing immunosuppression or a condition requiring immunosuppressive therap.⁸ Commonly associated conditions include Systemic Lupus Erythematosus Sjögren’s syndrome, dermatomyositis,⁹ myasthenia gravis, pemphigus vulgaris, ulcerative colitis, primary pulmonary hypertension, atopic dermatitis, Graves’ Disease,¹⁰ psoriatic arthritis,¹¹ Sézary syndrome, multiple IgA myeloma,¹² hypertriglyceridemia, hyperlipidemia,¹³ mycosis fungoides,⁸ and chronic myelogenous leukemia as well as patients with HIV, as seen in our case.^14,15 Many of the aforementioned conditions require immunosuppressive treatments such as corticosteroids or methotrexate, which may also be linked to MEDF though unclear mechanisms.¹⁶ It may be explained by the fact that these eruptive lesions result from an abortive immunoreactive process that can be triggered by the drugs that downregulate the T-cells.⁸ In the presence of MEDF, the likelihood of underlying immune mediated disease is as high as 83%.¹⁷ Therefore, further investigation and work up should be initiated for many immunologic conditions mentioned above when patients present with MEDF.

Differential Diagnoses

The differential for MEDF includes Kaposi’s sarcoma,¹⁸ also commonly seen in HIV patients, as well as malignant histiocytomas such as dermatofibrosarcoma protuberans (DFSP),⁷ eruptive xanthomas, and lymphoproliferative diseases.¹⁹ DF may clinically mimic Kaposi’s sarcoma.¹⁸ However, Kaposi’s sarcoma presents more commonly on the face and in the oral mucosa, which may help in differentiating the two.²⁰ Rare cases of DF may also present in the oral mucosa though, further complicating clinical diagnosis and sites.²¹ Malignant cutaneous DF are quite rare, but some reported cases of distant metastasis of malignant fibrous histiocytoma to the skin reminds that one must also rule out underlying malignancy and metastatic disease.²² Additionally, DF resembles DFSP superficially, but histologically distinct. DFSP are typically much more cellular, have a marked storiform pattern, invade and involve the subcutis deeply, often entrapping fat as it dives and proliferates along the subcutaneous septae on histology.⁷ It has been noted that the early phase of DFSP can simulate DF, particularly the deep and cellular forms of DF, sometimes leading to misdiagnosis.¹ Although DF often can be diagnosed clinically, skin biopsy with histopathologic examination provides the most reliable diagnosis and delineation of clinically similar lesions.

Treatment and Case resolution

DF are benign lesions with excellent prognosis; therefore, they generally do not require any treatment. It can be completely removed with surgical excision though recurrence has been reported.⁷ The patient should be advised to monitor lesions for any changes which may necessitate further work up.

In this case, reassurance was provided, and patient opted for continued observation as pruritis improved with application of moisturizer.

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22. Lew W, Lim HS, Kim YC. Cutaneous metastatic malignant fibrous histiocytoma. J Am Acad Dermatol. 2003 Feb;48(2 Suppl):S39-40. doi: 10.1067/mjd.2003.113. PMID: 12582384.