Case Presentation: Merkel cell carcinoma (MCC) is a rare neuroendocrine malignancy, with high propensity to metastasize and reoccur. It most commonly affects the skin, and seldomly involves internal organs [1]. MCC is a rare entity, with 2488 cases/year in 2013 in the United states and more aggressive than melanoma [1, 2]. Gaining insight into this carcinoma will allow for timely recognition, diagnosis and treatment.Dermatomyositis (DM) is an inflammatory myopathy with degenerative changes of the skin and muscles. It can present as a paraneoplastic phenomenon in setting of underlying malignancy, first described by von Hebra in 1868 ([3-5]. We present a rare case of MCC-induced paraneoplastic DM.A 48-year-old Caucasian female with past medical history of hypothyroidism and vitamin D deficiency presented with a rash affecting her face, neck, chest, arms and thighs for 6 months. Initially, Dermatology deemed this as an allergy to a new perfume and treated her with topical Metronidazole without relief. Around the same time, she began to develop arthralgias and myalgias, which raised the concern for DM and referral to Rheumatology. Her exam was evident for Gottron papules, shawl sign, holster sign, periungal erythema, telangiectasias, and dilated capillary loops. Her muscle strength was 5/5 but she complained of subjective myalgia and weakness. Her labs were negative for SSA, SSB, ANA, RNP, Jo1, ESR, CRP, anti-TIF1, MI-2, SRP, MDA-5, NXP-2, SPEP/UPEP, CK and aldolase. Skin biopsy of her hands showed dermatitis with dermal mucin deposition, consistent with DM. She was started on Prednisone initially and then steroid sparing agents Hydroxychloroquine and weekly Methotrexate were added. Given the concern for underlying malignancy, workup was initiated and included CT chest, abdomen and pelvis revealing left inguinal lymphadenophathy. Excisional biopsy revealed high grade neuroendocrine carcinoma with perinuclear dot-like positivity for CK20, consistent with MCC, with unknown primary. Other differentials included primary neuroendocrine neoplasms of salivary gland, ovary, and lung. Initial PET scan showed multiple enlarged hypermetabolic suspect lymph nodes in the left inguinal area. She received several cycles of Carboplatin and Etoposide, with allergic reaction to Etoposide. As second line treatment Pembrolizumab was added with good response, however, she had a flare in her DM and she was treated with Prednisone with Pembrolizumab held temporarily. For her DM, she continued on Hydroxychloroquine daily and Methotrexate weekly and once her flare resolved the Prednisone was tapered. Her follow-up PET scan revealed decreased metabolic activity within her pelvis and inguinal lymph nodes, without evidence of progressive malignancy. She continues to follow-up with Oncology.
Discussion: MCC can present as DM, making it challenging to establish this diagnosis. Russo et al. reported in their case series the association between DM and gynecological malignancy [6].
Conclusions: Patients presenting with DM, should be worked up for possible underlying malignancy labs and complete imaging studies. Biopsy should be done on any suspicious lesions. Approximately 20-30% of DM patients have a neoplasms [7]. Therefore, DM can be a consequence when cancer is not considered at time of presentation.