Straight Edge Sign: Radiographic Clues for Pulmonary Manifestations of Antisynthetase Syndrome

Abstract

This is a case of a 24 year old previously healthy African American female who presented with acute hypoxic respiratory failure secondary to a flair up of connective tissue disease related interstitial lung disease CTD-ILD secondary to anti-synthetase syndrome. CASE PRESENTATION: A 24 year old healthy female, with a strong family history of autoimmune diseases and no exposure history, presented to the Emergency Department with a 1 month history of progressive dyspnea and polyarthralgias. She was found to be febrile and in acute hypoxic respiratory failure requiring high flow oxygen. Physical exam revealed bibasilar inspiratory dry crackles, hyperpigmentation of the interphalangeal joints. Plan films demonstrated bilateral lower lobe opacities and she was admitted to the intensive care unit and treated empirically for pneumonia with minimal clinical improvement. Computed tomography demonstrated bilateral ground glass opacities with a positive straight edge sign. Due to concern for underlying autoimmune disease, empiric steroids were administered with improvement in symptoms. Subsequent autoimmune workup was notable for elevated creatinine phosphokinase and aldolase. Pulmonary function demonstrated restriction with severe diffusion impairment. Muscle biopsy demonstrated findings consistent with inflammatory myopathy. She continued to improve on steroids and was discharged to follow up as an outpatient for evaluation of steroid sparing therapy.DISCUSSION: Antisynthetase syndrome is a constellation of clinical findings frequently associated with polymyositis and dermatomyositis and occurs in the setting of other autoimmune diseases with interstitial lung disease, as apparent in our care. A recent paper published in 2018 suggested three radiological patterns of Usual Interstitial Pneumonia which might suggest an underlying connective tissue disease versus idiopathic pulmonary fibrosis. These signs include anterior upper lobe, exuberant honeycombing, and the straight edge sign with the latter manifesting in 25% of patients with CTD vs. 6% in ILD with a 4.22 positive likelihood ratio and a specificity of 94%. The straight-edge sign is a CT finding characterized by a fairly straight interface between fibrosis and normal lung tissue orthogonal to the lateral surface of the lung. Recognizing these signs clues the diagnosis in the undifferentiated patient towards earlier treatment of hypoxemia, further appropriate autoimmune workup, reducing antimicrobial exposure in the setting of positive SIRS criteria, and allows earlier initiation of immunosuppressants.CONCLUSIONS: This case is supportive of detecting radiographic signs of connective tissue disease, as manifested with straight-edge sign to guide earlier diagnosis of CTD-ILD and prompt medical treatment in the acute inpatient and chronic outpatient settings.