Primary Biliary Cholangitis Presenting with Low Back Pain and Complicated by Immune-Mediated Necrotizing Myositis: A Case Report.

Primary biliary cholangitis (PBC) and immune-mediated necrotizing myositis (IMNM) are both rare autoimmune disorders, and their coexistence is uncommon. Low back pain (LBP) as the initial presentation of this overlap is extremely rare and may delay diagnosis. A case is presented of a 46-year-old woman with recurrent LBP and mild proximal muscle weakness, along with laboratory findings of elevated liver and muscle enzymes, positive anti-mitochondrial antibody subtype M2 (AMA-M2), anti-GP210, and anti-SSA antibodies, and negative myositis-specific antibodies. Imaging revealed paraspinal myositis, and histopathology confirmed PBC (stage 1) and IMNM. The patient responded well to a combination of ursodeoxycholic acid, corticosteroids, hydroxychloroquine, and mycophenolate mofetil, achieving normalization of laboratory parameters and complete symptom resolution after 15 months. This case underscores the need for clinicians to consider systemic autoimmune diseases in patients with atypical LBP and highlights the potential for AMA-M2-positive myositis to involve the paraspinal muscles, providing insight into a rare manifestation of PBC-IMNM overlap. Cite this article as: Zhu L, Yan T, Ye Q. Primary biliary cholangitis presenting with low back pain and complicated by immune-mediated necrotizing myositis: A case report. Eur J Rheumatol. 2026, 13(1), 0050, doi:10.5152/eurjrheum.2026.25050.