Anti-Ku antibodies were identified in an adolescent patient with systemic sclerosis (SSc)-polymyositis overlap syndrome, according to a case report published in Pediatric Dermatology.
A 13-year-old girl presented with symmetric proximal muscle weakness that had developed over several years and was associated with tightness and shininess of the skin on her arms, legs, and anterior upper chest and decreased skin laxity on her hands and feet. The patient had a history of epilepsy which was well-controlled with lamotrigine and carbamazepine.
Creatine kinase (10,840 IU/L), adolase (144.1 U/L), lactate dehydrogenase (4114 IU/L), aspartate aminotransferase (318 IU/L), and alanine aminotransferase (190 IU/L) levels were all elevated. Antinuclear antibodies were present at a dilution >1:2560. Skin punch and muscle biopsies were performed at the shoulder and the right vastus lateralis, which revealed homogenization, sclerosis, and thickening of the dermis, as well as nonspecific inflammatory and dystrophic changes, respectively.
The patient received genetic testing but a causative mutation was not identified. A myositis-associated antibody panel was also performed, which isolated anti-Ku antibodies; these antibodies are not commonly associated with SSc-polymyositis overlap syndrome that has primarily been linked to anti-PM/Scl autoantibodies.
The patient received daily prednisone (1 mg/kg, oral) and weekly methotrexate (0.5 mg/kg, subcutaneous). The prednisone dose was tapered over time. Within 12 months, the patient’s muscle strength returned to normal, and her skin changes resolved within 16 months.
Authors of the report noted that anti-Ku-associated SSc-polymyositis overlap syndrome was rare, particularly in children.
“Our report underscores the importance of testing for anti-Ku antibodies specifically in patients with myositis and SSc suggestive of this syndrome.”
Loo RJ, Nocton JJ, Harmelink MM, Chiu YE. Anti-Ku antibody-positive systemic sclerosis-polymyositis overlap syndrome in an adolescent [published online June 10, 2020]. Pediatr Dermatol. doi:10.1111/pde.14243