Three cases of immune‐mediated necrotizing myopathy with anti‐signal recognition particle antibodies: Extramuscular symptoms preceding progressive muscle weakness

Abstract

Background Immune‐mediated necrotizing myopathy with an anti‐signal recognition particle antibody (anti‐SRP myopathy) is generally refractory to treatment. Anti‐SRP myopathy is characterized by muscle weakness as the main symptom, but is often complicated by extramuscular symptoms. Rarely, the extramuscular symptoms precede muscle weakness. In the present report, we describe the clinical presentation and medical history of three patients with extramuscular symptoms. Focusing on the extramuscular symptoms, anti‐SRP antibody‐positive myopathy can be diagnosed at an early stage. It might therefore be treatable before muscle weakness progresses. Case presentation Patient 1 was a 68‐year‐old woman who suffered progressive muscle weakness after a 2‐year history of creatine kinase elevation, vitiligo, 1‐year history of easy fatigability, sinus insufficiency and a 6‐month history of myalgia. She was followed up in the cardiology department. Patient 2 was a 77‐year‐old woman who showed muscle weakness and respiratory failure after a 3‐day history of malaise, loss of appetite and creatine kinase elevation. She initially visited the internal medicine department and was suspected of having heat stroke at the first visit. Patient 3 was a 48‐year‐old man who had a gastric ulcer and progressive weakness after a 1‐year history of anorexia and severe weight loss. He first visited the gastroenterology department. Conclusions All three patients visited the internal medicine department before the neurology department. It is important to consider anti‐SRP myopathy as a differential diagnosis for patients presenting with elevated creatine kinase levels and extramuscular symptoms.