Cervical Actinomycosis Diagnosed via Metagenomic Next-Generation Sequencing of Formalin-Fixed Paraffin-Embedded Tissue: A Case Report and Literature Review

Actinomycosis is an uncommon but significant chronic bacterial infection affecting various parts of the body caused by <i>Actinomyces</i> species. Because of the nonspecific symptoms and rarity of the condition, the diagnosis of head-and-neck or cervicofacial actinomycosis is usually challenging and delayed. A 39-year-old woman presented with an enlarging right neck mass and dysphagia after steroid exposure for treatment of De Quervain thyroiditis. MRI showed a large irregular infiltration mass over the right side of her neck, with a multi-loculated rim-enhancing area over the right retropharyngeal space. Excisional biopsy of the lesion only showed evidence of acute on chronic inflammation, and the results of all microbiological testing (including bacterial culture, Gram-staining, and molecular detection) were negative. Metagenomic next-generation sequencing (mNGS) of the formalin-fixed paraffin-embedded (FFPE) tissue from the patient was performed. DNA of <i>Actinomyces israelii</i> and <i>Methylobacterium</i> was detected. The patient was confirmed to have cervical actinomycosis and completely recovered after 6 months of oral amoxicillin. Our patient is the first case utilizing mNGS on FFPE tissue to diagnose cervical actinomycosis. This case shows that mNGS is a promising, unbiased tool for detecting <i>Actinomyces</i> species in FFPE tissues and diagnosing cervical actinomycosis. It also highlights the diagnostic difficulties of cervical actinomycosis.