Polyarteritis nodosa initially presenting as concomitant peripheral neuropathy and myositis in unilateral limb: A case report.

Rationale: We report the case of a patient who initially presented with peripheral neuropathy and myositis without typical organ involvement, such as the kidneys, skin, or gastrointestinal system, but was ultimately diagnosed with polyarteritis nodosa (PAN).

Patient Concerns: A 62-year-old man presented with radicular pain in his right lower extremity. One week later, he complained of right ankle motor weakness and pain in the right posterior thigh, which led to admission. After 6 weeks of hospitalization, he newly experienced pain in his right testicle and anterior thigh.

Diagnosis: The patient was initially diagnosed with polymyositis combined with sciatic neuropathy using magnetic resonance imaging, electrodiagnostic tests, and muscle biopsy. However, with the emergence of other systemic symptoms such as testicular pain, vasculitis was suspected, and the patient was reclassified as PAN using the 2007 European Medicines Agency algorithm and the American College of Rheumatology criteria.

Interventions: The patient was treated with glucocorticoids for more than 6 months, and antiviral medication was prescribed to prevent hepatitis B virus reactivation.

Outcomes: The patient's radicular pain and pain in the right anterior and posterior thighs and testicle improved, and there were no signs of recurrence.

Lessons: In patients presenting with radicular and focal muscle pain, it is crucial to consider the potential for PAN, as observed in this case report.