# Polymyositis-Like Myopathy With Anti-PL-12 Antibody Positivity and Coexisting Antiphospholipid Syndrome: Diagnostic and Management Challenges in the Absence of Systemic Features

## TL;DR

A case of polymyositis-like myopathy with anti-PL-12 antibodies and antiphospholipid syndrome is presented, highlighting diagnostic challenges and treatment in the absence of typical systemic features.

## Contribution

This case report highlights the importance of muscle biopsy in diagnosing anti-synthetase syndrome with atypical presentations and coexisting antiphospholipid syndrome.

## Key findings

- Muscle biopsy confirmed immune-mediated myopathy despite absence of typical systemic features.
- Combination therapy with prednisone and mycophenolate mofetil led to clinical and biochemical improvement.
- The case illustrates the variability in anti-synthetase syndrome presentations and the need for multidisciplinary management.

## Abstract

Polymyositis-like inflammatory myopathies are a rare subset of idiopathic inflammatory myopathies (IIMs) characterized by proximal muscle weakness, elevated muscle enzymes, and immune-mediated skeletal muscle damage. These conditions are often associated with myositis-specific autoantibodies (MSAs), such as anti-alanyl-tRNA synthetase antibody (anti-PL-12), which define subtypes like anti-synthetase syndrome. We present the case of a 50-year-old female patient with progressive proximal muscle weakness, elevated creatine kinase and aldolase levels, and serological evidence of anti-PL-12 antibodies. Muscle biopsy revealed hallmark findings of immune-mediated myopathy, including increased sarcolemmal major histocompatibility complex class I (MHC1) expression, vascular membrane attack complex (C5b-9) deposition, and focal myofasciitis. Despite the absence of hallmark systemic features of the anti-synthetase syndrome, such as interstitial lung disease (ILD) or arthritis, these findings confirmed a diagnosis of polymyositis-like myopathy within the anti-synthetase syndrome spectrum.

The patient’s concurrent antiphospholipid syndrome (APS) necessitated careful anticoagulation management while initiating immunosuppressive therapy with prednisone and mycophenolate mofetil, which led to clinical and biochemical improvement. This case underscores the diagnostic challenges posed by incomplete phenotypes of anti-synthetase syndrome and the critical role of muscle biopsy in confirming autoimmune myopathies. By illustrating the variability of presentations and the necessity of a multidisciplinary approach, this report contributes to the understanding and management of complex autoimmune myopathies.