The Diagnosis of Signal Recognition Particle-Associated Immune-Mediated Necrotizing Myopathy Requires the Exclusion of Possible Differential Diagnose
Year: 2025
Type: article
Abstract: Dear Editor, We read with interest the article by Huang et al. about a 33-year-old woman with immune-mediated necrotizing myopathy (IMNM) who was diagnosed based on clinical presentation, elevated muscle enzymes, a muscle magnetic resonance imaging (MRI), and the presence of antibodies to the signal recognition particle (SRP).[1] The patient was treated with glucocorticoids, but only incomplete recovery was achieved at the 2-year follow-up.[1] The study is impressive, but some points need to be discussed. The first point is that the diagnosis of IMNM remained unsupported. IMNM was not confirmed by a muscle biopsy. A biopsy is useful to demonstrate the inflammatory process and necrosis of the myofibers. The apparent improvement of the clinical deficits under glucocorticoids does not necessarily support the suspected diagnosis, as it could also be a spontaneous improvement not necessarily due to the glucocorticoids. Furthermore, MRI of the muscles with T1 hyperintensity and T2 hyperintensity does not necessarily indicate inflammation alone. What lacks in this regard are T1-weighted images with contrast agent. IMNM may show up as enhancement on MRI.[2] The second point is that after 2 years, hyper-creatinine kinase emia and a waddling gait were still present, despite continued use of prednisolone and azathioprine.[1] Was IMNM confirmed by muscle biopsy during these 2 years? It should also be discussed whether the long-term use of prednisolone was responsible for the persistent hyperkalemia and waddling gait? Steroid myopathy is clinically characterized by proximal muscle weakness.[3] The third point is that a negative family history does not rule out a hereditary neuropathy. If a comprehensive search for the secondary causes of neuropathy is negative, genetic testing should be considered. Since no case of anti-SRP-associated neuropathy has been reported so far, it is quite unlikely that the neuropathy in the index patient was actually caused by anti-SRP. Furthermore, there is hardly any literature on neuropathy associated with myositis-specific antibodies.[4] Based on these considerations, a causal relationship between anti-SRP and neuropathy is rather unlikely. The fourth point is that the patient did not undergo a nerve biopsy. Since neuropathy in IMNM has only been reported in patients with polyangitis,[5] it could have been useful to perform a nerve biopsy after a comprehensive search for primary and secondary causes of neuropathy was negative. The fifth point is the discrepancy between the symptoms, such as numbness in both lower limbs, and the clinical examination, which shows absent tendon reflexes in the lower limbs but no sensory deficits. Were both superficial and deep sensory qualities really intact? Was a quantitative sensory examination performed? In conclusion, it can be said that this interesting study has limitations that relativize the results and their interpretation. Addressing these limitations could strengthen the conclusions and corroborate the study’s message. Before diagnosing anti-SRP-related axonal neuropathy, it is essential to establish a clear causal link. In patients who do not fully recover from clinical and laboratory signs of IMNM, re-examination with all available diagnostic tools, including muscle and nerve biopsy, should be considered. Data availability statement Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
Source: Acta Neurologica Taiwanica
Author: Josef Finsterer
Institution: University of Vienna
Language: English
Subfield: Epidemiology
Field: Medicine
Domain: Health Sciences
Open Access status: diamond
OpenAlex ID: W4408920519