Case Report: Nocardia farcinica infectious arthritis and myositis in an immunocompromised host: diagnostic and management challenges.

BACKGROUND: Nocardia farcinica is a rare opportunistic pathogen predominantly affecting immunocompromised hosts. Infectious arthritis, cutaneous and deep soft tissue infections caused by this organism often present with nonspecific clinical manifestations. Additionally, due to its slow-growing and oligotrophic nature, both cultivation and identification pose considerable challenges, thereby complicating clinical diagnosis and management.

CASE PRESENTATION: This case report described an elderly female patient presenting with right shoulder redness, swelling, and pain. Her history included diabetes, local corticosteroid injections, and newly identified humoral immunodeficiency (hypogammaglobulinemia with low B-cell count). Imaging revealed infectious arthritis of the right shoulder, accompanied by infectious myositis and an intermuscular abscess in the right upper arm. Nocardia farcinica was confirmed by metagenomic next-generation sequencing (mNGS) and culture of aspirated fluid. Initial therapy with trimethoprim-sulfamethoxazole (TMP-SMX) and ceftriaxone was limited by renal impairment and gastrointestinal intolerance, and susceptibility testing indicated TMP-SMX resistance. Treatment was switched to linezolid. Due to inadequate clinical response, multiple surgical debridements were performed. Subsequently, therapy was changed to oral minocycline because of linezolid-induced bone marrow suppression and intolerance. At discharge, the maintenance regimen consisted of moxifloxacin combined with minocycline.

CONCLUSION: This case highlights the importance of considering low-virulence pathogens such as Nocardia in immunocompromised patients with atypical infections that respond poorly to initial empiric therapy. Pathogen identification, aided by tools like mNGS for rapid detection, is essential. When classic regimens are limited by adverse effects, susceptibility-guided alternative therapies can be effective. For localized infections refractory to medical management, multidisciplinary surgical intervention remains a critical component of care.