Plaque-like cutaneous mucinosis associated with pain: A case report

Abstract

Plaque-like cutaneous mucinosis (PCM) is a rare atypical subtype of Lichen myxedematosus, characterized by hyperpigmented plaques typically found on the midline trunk. We report the case of a 26-year-old woman with a 1-year history of painful, pruritic, hyperpigmented plaques over her spine. Physical examination revealed soft plaques in the midline of the back, and histopathology showed dermal mucin deposition, consistent with PCM. The presented case is notable as the first reported instance of PCM presenting with lesional pain. We propose that mechanical stress, likely due to repeated friction at the site of spinous processes, contributed to the development of pain. The fact that pain lessened after the use of a lumbar support pillow and gaining weight supports our hypothesis. Our case demonstrates the importance of considering PCM in the differential diagnosis of hyperpigmented plaques and highlights the need for further research to elucidate its underlying pathogenesis and optimize treatment strategies.

Introduction

Plaque-like cutaneous mucinosis (PCM) is a rare atypical subtype of Lichen myxedematosus, characterized by the abnormal accumulation of mucin in the dermis, resulting in distinctive clinical and histopathological features.^1–3 The pathogenesis of PCM remains poorly understood, it is highly probable that PCM comprises a heterogeneous group of disorders with mucin accumulation rather than a single entity. ² PCM affects females more than males, with a ratio of 4:1, and often begins between the third and fifth decades of life. ² Most patients with PCM have no underlying systemic disorders, although a link with malignancies has been observed in a number of patients, particularly with adenocarcinomas of the lung, colon, breast, and pancreatobiliary system.^4–6 Recently an association with central giant cell granuloma with a KRAS mutation has been identified. ⁷ However, it is suggested that this likely represents a chance association.^2,8

Histopathologically, PCM is characterized by focal or diffuse interstitial mucin accumulation in the dermis, dermal edema, and superficial perivascular lymphocytic infiltration. ² Dermal mucin stains with Alcian blue at pH 2.5, colloidal iron and is periodic acid–Schiff-negative. ⁹

PCM lesions may improve after decades, but spontaneous resolution has been rarely described. ⁶ Pharmacological interventions, including antimalarials (chloroquine, hydroxychloroquine, and quinacrine), antihistamines (pyrrobutamine and methapyrilene), and topical and systemic corticosteroids, have been reported in the literature with varying degrees of success. ² Plaques in PCM are noted to be particularly concentrated over the midline of the back and chest. The plaques are typically asymptomatic but could be associated with pruritus. ²

Here we describe an unusual presentation of PCM when lesions on the back of a 26-year-old female patient were accompanied by pain. To the best of our knowledge, pain has not been described in the literature and is a novel clinical finding in PCM.

Case presentation

An otherwise healthy 26-year-old woman presented to a Dermatology clinic with a 1-year history of hyperpigmented plaques over her spine associated with pruritus, burning sensation, and pain. She reported that pain was being intensified while she was touching the seatback with her back.

Patient initially visited her family physician with complaints of a painful reddish rash on her back and was treated with acyclovir due to the suspected diagnosis of herpes zoster, without any improvement. However, her symptoms persisted and worsened over time, with new lesions appearing and old ones expanding and darkening in color. According to the patient, malignancy and tuberculosis were excluded after an extensive workup (unknown to us). However, no definitive diagnosis was reached. No treatments were attempted before she sought further evaluation at our clinic.

Physical examination revealed hyperpigmented plaques along the midline of the back, located exactly at the most prominent areas of the spine (Figure 1(a)), which were tender upon palpation, no other body sites were affected. No lymphadenopathy was observed. A rheumatologic review of systems, including assessment for oral ulcers, and signs of arthritis, yielded negative results. Patient was underweight (body-mass index (BMI) 16.1 kg/m²) due to pure eating habits. The main clinical differential diagnoses were PCM, hyperpigmented morphea, and tumid lupus erythematosus.

Figure 1.

(a) Initial presentation. Multiple painful, pruritic, hyperpigmented, soft plaques in the midline of the back; (b) follow-up examination 2 months after initiating treatment. Reduction in plaque thickness and decreased hyperpigmentation; (c) follow-up examination 1 year later, there are no noticeable skin findings present.

Blood tests, including a complete blood count, erythrocyte sedimentation rate, and C-reactive protein, were normal. Autoimmune screens, such as the antinuclear antibody test, anti-Smith, anti-Ro/SSA, anti-La/SSB, and anti-Scl-70 were negative or normal. Serum and urine protein electrophoresis revealed no monoclonal gammopathy. High-resolution soft tissue ultrasonography showed non-demarcated complex subcutaneous masses.

A single 4-mm punch biopsy was obtained and sent for histopathological examination, which revealed a normal epidermis, and mild upper and deep dermal perivascular inflammatory cell infiltrate composed mainly of lymphocytes. Multifocal areas of mucin deposition were observed, separating collagen fibers in the mid to deep dermis and extending into the subcutis. Colloidal iron staining confirmed mucin deposition throughout the dermis.

Based on clinical and histological findings, the patient was diagnosed with PCM, and a topical steroid, betamethasone valerate 0.1% ointment twice a day, were prescribed. She was advised to use a chair with a soft back or lumbar support pillow to avoid mechanical pressure from a hard seat back. Additionally, she was referred to a nutrition specialist for dietary counseling.

During the follow-up examination 2 months after initiating treatment, her BMI slightly increased to 16.8 kg/m². Furthermore, there was a reduction in plaque thickness on her back, accompanied by the resolution of pain and decreased hyperpigmentation (Figure 1(b)). During the follow-up examination 1 year later, there are no noticeable skin findings present (Figure 1(c)), the patient continues to use a lumbar support pillow as the hard surface of the chair still produces a slight burning sensation in the areas of former lesions.

Discussion

PCM remains a rare and poorly understood condition characterized by the abnormal accumulation of mucin in the dermis, with a significant clinical heterogeneity, with most cases considered reactive processes rather than primary disorder. Histopathological examination is crucial for confirming the diagnosis of PCM.

Presented case adds to the growing body of literature surrounding PCM, particularly emphasizing the novel presentation of associated lesional pain, which has not been previously documented. We believe that mechanical stress, likely due to repeated friction or pressure at the site of spinous processes, contributed to the development of pain in our patient, suggesting a potential link between mechanical stimuli and the pathogenesis of PCM. It has long been known that, when skin is subjected to mechanical stress its properties may be altered, and these changes may make disease more likely. ¹⁰ Also many normal biochemical functions of the skin are dependent on appropriate mechanical forces, and when these become excessive, various mediators are released with many deleterious consequences. It is known that fibroblasts of different subsets act as heterogeneous responders to mechanical load. ¹¹ We think that the mechanical pressure could have acted as an antigenic stimulus and the deposition of mucin. The resolution of pain and reduction of plaque thickness following patient’s weight gain and continuous use of a lumbar support pillow further support this hypothesis. Further research is warranted to elucidate the underlying pathogenesis of PCM and cutaneous mucinosis in general.

While treatment options for PCM are limited, our case demonstrates the potential efficacy of topical corticosteroids in managing associated symptoms.

Conclusion

In conclusion, our case report highlights an unusual presentation of PCM with associated lesional pain, which to our knowledge, has not been previously documented in the literature. We propose a potential link between mechanical stress and the pathogenesis of PCM, suggesting that repeated friction or pressure at the site of spinous processes may contribute to the development of pain and mucin deposition. While treatment options for PCM are limited, our case demonstrates the potential efficacy of topical corticosteroids in managing associated symptoms. Overall, the presented case underscores the importance of recognizing PCM as a differential diagnosis in patients presenting with hyperpigmented plaques and highlights the need for further research to elucidate its underlying pathogenesis and optimize treatment strategies.