A Case of Dermatomyositis associated with Antibodies against SUMO Activating Enzyme (SAE)

Clinical Other
16
Anthony Bradshaw, MD, Francy Shu
1. University of California, Los Angeles (UCLA), 2. UCLA

Background:
Myositis-specific autoantibodies are increasingly used in the classification of inflammatory myopathies to predict distinct clinical phenotypes and disease prognosis. Among patients with dermatomyositis (DM), antibodies against small ubiquitin-like modifier activating enzyme (SAE) are the least frequently encountered, identified in less than 10 percent of patients.

Objectives:
We describe a patient with SAE antibody-associated DM, highlight its distinct clinical features, and emphasize the importance of timely therapy.

Approach:
An 80-year-old woman presented with a two-year history of progressive gait decline, proximal limb weakness, and myalgia, followed by a head drop and dysphagia with 60-pound weight loss, requiring gastrostomy tube placement. Examination showed heliotrope eruptions and hyperpigmented plaques and scales in the neckline, torso, and legs. Significant pruritus had resulted in lichen simplex chronicus. Pertinent neurologic findings included MRC grade 4/5 strength in the neck extensors, 2/5 in bilateral deltoids and iliopsoas, 4/5 in biceps, triceps, and gluteus medius, and 4+/5 in quadriceps, hamstrings, and adductors. Reflexes were symmetrically 1+ in biceps and patellae and absent elsewhere.

Results:
Laboratory evaluation showed normal CK and aldolase, elevated ANA (1:640) with speckled pattern, and strongly positive SAE antibodies. MRI of the bilateral femurs showed diffuse muscle edema, most pronounced in the quadriceps, and mild fatty atrophy of distal thigh muscles. Treatment with high-dose prednisone and methotrexate resolved her head drop and improved her limb strength and rash.

Conclusions:
SAE antibody-associated DM is an under-recognized subtype characterized by axial and proximal limb weakness, pruritic rash, and severe dysphagia in up to 75 percent of cases. Interstitial lung disease occurs in 50 percent and malignancy in 20 percent of cases. A timely and accurate diagnosis is the cornerstone to effective treatment.