Dermatomyositis: A Rare Presentation of Metastatic Prostate Cancer

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<strong>Background:</strong> Dermatomyositis (DM) is an idiopathic inflammatory myopathy with various cutaneous manifestations. There is a strong association between DM and malignancy with an estimated 5–7 fold increase in cancer incidence in DM patients compared to the general population. Dermatomyositis as a paraneoplastic manifestation has been reported in several malignancies notably ovarian, gastric, colon, cervical, pancreatic, and lung cancer but rarely in prostate cancer (<em><strong>Table 1</strong></em>). <strong>Case Presentation:</strong> A 64-year-old male with a past medical history of hypertension, gout, and type II diabetes was admitted to the hospital following a mechanical fall after which he sustained shoulder and facial trauma. On further evaluation, the patient was found to have dysphagia, dysphonia, proximal upper extremity and lower extremity weakness, and rashes. The dysphagia began one month prior to presentation and the rashes appeared two months prior. Physical exam was notable for erythematous and scaly-dry skin in V-neck pattern, gottron papules, facial and periorbital erythema with scaly skin, periungual erythema, oropharyngeal salivary pooling, proximal bilateral upper and lower extremity weakness with intact distal extremity strength, and wasting of the bilateral quadriceps and hamstrings. Labs were notable for elevated creatine kinase (CPK) 296, positive Anti-p155/140 antibodies which are directed against transcription intermediate family-1 (TIF-1). Further workup with a computed tomography scan (CT) of the abdomen and pelvis revealed extensive pelvic and abdominal lymphadenopathy, centered in the pelvis, and therefore suspicious for either nodal metastasis from prostate adenocarcinoma versus lymphoma. A right inguinal lymph node biopsy was done and confirmed the diagnosis of metastatic adenocarcinoma of the prostatic primary. Staging workup via bone scan and MRI showed diffuse osseous metastases in the thoracolumbar spine (<em><strong>Figure 1</strong></em>). Consequently, the patient was started on Bicalutamide and Leuprolide as therapy for the underlying prostate cancer by the inpatient oncology team. The neurology service was consulted for the muscle weakness and were immediately concerned for dermatomyositis. Hence, they recommended empiric treatment with steroids whish were initiated and a biopsy of the left deltoid muscle was obtained. Biopsy results revealed skeletal muscle with perifascicular atrophy and mild mixed inflammatory infiltrate, suggestive of DM (<em><strong>Figure 2</strong></em>). Hence, in the setting of the patient’s clinical presentation confirmed the diagnosis of DM likely paraneoplastic. The patient was started on intravenous immunoglobulins (IVIG) in addition to steroids for treatment of DM. The patient’s hospital course was complicated by worsening dysphagia necessitating percutaneous gastric tube placement (PEG), worsening dysphonia, as well as hypoxic respiratory failure requiring a brief intensive care unit admission and non-invasive positive pressure ventilation. The patient slowly regained his speech and his respiratory status improved. He was able to be discharged to a subacute rehab after 37 days of inpatient stay. The patient is still requiring a PEG tube for feeding but his dysphagia has significantly improved, and his rashes have almost resolved. His muscle strength is slowly recovering. He continues to get IVIG sessions and steroids as well as Leuprolide injections every three months for treatment of his metastatic prostate cancer. His prostate-specific antigen (PSA) a marker that is usually elevated in prostate cancer and was markedly elevated in this patient began to downtrend significantly which usually indicates a positive response to therapy. <strong>Conclusion:</strong> This case illustrates the importance of screening for an underlying malignancy in any patient presenting with DM. Because of the rarity of DM physicians should maintain a high index of suspicion and screen for more cancers than only those reported to be commonly associated with DM. Cases have shown that systemic manifestations of paraneoplastic DM tend to improve following treatment of the underlying malignancy.