Large cellulitis‐like erythematous plaques with overlying nodules on bilateral shins

A 73-year-old man with no history of thyroid disease presented with a 1-year history of asymptomatic erythematous to orange papules on bilateral shins, which gradually progressed into large reddish plaques. Examination revealed large cellulitis-like shiny and infiltrative erythematous plaques with a nodular surface and scattered scaling on the anterior and lateral aspects of the legs. Varicosities were also noted on bilateral dorsal feet (Figure 1). A skin biopsy was performed to confirm the diagnosis. Your diagnosis? … Diagnosis: Euthyroid pretibial mucinosis (EPM) Histopathology showed epidermal atrophy with slight laminated orthokeratosis. The upper dermis was edematous with proliferation of spindled and occasional stellate shaped fibroblasts associated with many loosely lobulated and some vertically oriented small blood vessels, and a sparse lymphocytic dermal infiltrate with pigmented macrophages and red blood cells extravasation. The reticular dermis showed a focal perifollicular lymphocytic infiltrate. Alcian blue pH 2.5 showed increased mucin in the upper dermis (Figure 2), which was digested by hyaluronidase. The endothelial lining of the vessels was mostly CD34-positive, while the spindle cells were CD34-negative. D2-40-positive lymphatic vessels were mainly located in the mid to lower dermis. Iron stain highlighted dermal hemosiderin deposits. The patient had been obese for approximately 4 years, with a body mass index (BMI) of 32 kg/m2. Laboratory findings showed normal thyroid function, with TSH, T3, and T4 levels within the reference range. Doppler ultrasonography on bilateral lower limbs showed dysfunctional venous valves with evidence of venous insufficiency. Lymphoscintigraphy showed partial obstruction of lymphatic drainage and mild lymphedema of the bilateral legs. A diagnosis of EPM was made, attributed to multiple contributing factors including stasis, obesity and lymphedema in our patient. He was treated with a topical steroid, oral pentoxifylline, and was referred to the Family Medicine outpatient clinic for weight reduction. Cutaneous mucinosis comprises a heterogeneous group of disorders characterized by abnormal deposition of mucin in the skin.1 EPM is characterized by mucin deposition in the dermis of the bilateral shins. Although the terms EPM and pretibial myxedema are often used interchangeably, the latter should be reserved for patients with autoimmune thyroid disease. EPM is associated with venous insufficiency, lymphedema, obesity, and local trauma.2-4 Clinically, patients typically present with asymptomatic, skin-colored to erythematous or yellowish, semi-translucent waxy papules on both shins. These papules may coalesce into plaques, often accompanied by bilateral leg edema. In some cases, the lesions exhibit a peau d'orange appearance.5 The pathogenesis remains unclear, but both lymphedema and venous insufficiency are thought to contribute via local tissue hypoxia, which stimulates fibroblasts to secrete mucin.2-4 Histopathology reveals epidermal thinning, the effacement of rete ridges, and mucin deposits in the papillary dermis, without a Grenz zone of normal collagen fibers. Subepidermal blisters may be seen in cases with prominent dermal edema. Dermal angioplasia with vertically oriented blood vessels in the upper to mid dermis is frequently noted. Other findings include hemosiderin deposits and spindled to stellate-shaped fibroblasts in the mucin deposition zone.6 Emerging conditions of acquired cutaneous mucinosis, such as stasis dermatitis and obesity-associated lymphedematous mucinosis,1, 4 highlight the diverse etiologies of pretibial mucinosis. However, these conditions should all be considered within the spectrum of EPM, given the significant overlap in their clinicopathological features. The main differential diagnosis of EPM is pretibial myxedema, a late manifestation of thyroid disease, particularly in patients with Graves’ disease. Pretibial myxedema presents with bilateral non-pitting, indurated nodules and plaques of variable color mainly affecting anterolateral legs. Prominence of hair follicles is commonly observed, resulting in a characteristic peau d'orange appearance, similar to that seen in EPM.6 Histopathology shows mucin deposition in the reticular dermis sparing the papillary dermis, widened space between the collagen bundles, stellate shaped fibroblasts, epidermal hyperkeratosis, papillomatosis and acanthosis. The location of mucin deposits helps differentiate pretibial myxedema from EPM. Besides, angioplasia and hemosiderin deposits, which are typical features in EPM are not seen in pretibial myxedema.6 Lichen myxedematosus can also present as cellulitis-like lesions on the legs,7 but histopathology shows fibroblast proliferation and dermal mucin deposition without vertically oriented dermal angioplasia.8 Management of EPM involves topical steroids and addressing underlying conditions. For obese patients, dietary modification and weight reduction are crucial. Compression therapy helps alleviate lymphedema and venous stasis. Surgical intervention may be necessary for refractory cases of stasis.4, 5 Pentoxifylline inhibits fibroblast proliferation and has demonstrated efficacy in patients with pretibial myxedema,9 although its effect in EPM appears limited.2 More recently, a case report demonstrated the potential efficacy of carbon dioxide laser therapy.10 This case underscores the importance of considering etiologies beyond autoimmune thyroid disease in patients presenting with pretibial mucinosis, thereby warranting a thorough clinical evaluation. None.