449 - Severe Functional Decline from Dermatomyositis Secondary to Prostate Adenocarcinoma Affecting the Bilateral Iliopsoas and Posterior Paraspinal Muscles

Case Diagnosis: Functional Decline from Dermatomyositis Secondary to Prostate Adenocarcinoma

Case Description: Eighty-four-year-old male presented to the hospital with six weeks of worsening bilateral lower extremity weakness, dysphagia, facial rash and swelling. Muscle biopsy confirmed diagnosis of dermatomyositis; right iliac lymph node biopsy confirmed metastatic prostate adenocarcinoma. Patient with positive antinuclear antibody(ANA) and transcriptional intermediary factor 1-gamma(TIF1-γ) antibody. Completed course of methylprednisolone and two cycles of IVIG. Lumbar spine MRI was obtained due to minimal improvement despite treatment, revealing inflammation and edema of bilateral iliopsoas and paraspinal musculature, consistent with severe myositis. PM&R was consulted for evaluation of worsening weakness; patient was found to have generalized motor weakness in upper and lower extremities, most severe with bilateral hip flexion graded at 3/5 and inability to do sit-to-stand.

Discussions: Autoimmune dermatomyositis is associated with six-fold higher risk of malignancy. Diagnosis is made by clinical criteria, MRI findings of muscle edema, and biopsy findings of chronic inflammation. TIF1-γ antibodies are myositis-specific and strongly associated with dermatomyositis and malignancy. Muscle weakness progresses over months with 50% muscle destruction required to cause symptomatic weakness, and is commonly symmetric, classically involving proximal muscles such as hips and shoulders that can be visualized on T1-weighted imaging. When chronic, fatty atrophy of musculature is seen, and subcutaneous connective tissue and fascia can also be involved, causing swelling and compression of nearby nerves and vessels. When dermatomyositis is driven by underlying malignancy, immunosuppressive therapy is often insufficient, and prompt treatment of the cancer should be initiated. Physical activity including therapies should be curtailed until inflammation subsides.

Conclusions: This case illustrates a unique presentation of dermatomyositis secondary to malignancy, with associated functional deficits due to significant inflammation and edema of bilateral iliopsoas and paraspinal musculature. Clinical importance of this case stems from understanding imaging findings of inflammatory myopathies and connecting these findings to clinical symptoms.