Systemic polyarteritis nodosa diagnosed in adulthood after childhood-onset recurrent inflammatory disease with atypical Still-like features: a case report

We report a rare long-term case in which systemic polyarteritis nodosa (PAN) was ultimately diagnosed in adulthood after childhood-onset recurrent inflammatory disease with atypical Still-like features. A Japanese man had recurrent febrile episodes from infancy and was diagnosed with juvenile idiopathic arthritis at 9 years of age. In early adulthood, he developed recurrent fever, rash, polyarthralgia, splenomegaly, neutrophilia, and elevated inflammatory markers, and was considered to have Still-spectrum disease. However, ferritin elevation remained modest despite marked systemic inflammation, suggesting that the early phenotype may not have represented typical Still's disease and may instead have reflected a broader autoinflammatory process. At 25 years of age, he developed digital ischaemia with necrosis, palpable nodules, and erectile dysfunction. Angiography demonstrated narrowing of the ulnar and palmar arteries, and skin biopsy showed necrotising vasculitis involving medium-sized vessels, leading to the diagnosis of systemic PAN. He subsequently developed fever, rash, inner-ear involvement, hypertrophic pachymeningitis, and tortuosity/dilatation of a right intercostal artery. A subtle suspected lesion of the right testicular artery later became a definite enlarging aneurysmal lesion on serial imaging. Systemic inflammatory manifestations were subsequently controlled during treatment that included glucocorticoids, azathioprine, and tocilizumab. However, serial imaging demonstrated gradual enlargement of the right testicular artery aneurysmal lesion despite the absence of fever, rash, or C-reactive protein elevation for 5 years. This clinical course suggests that vascular progression may not always be adequately reflected by C-reactive protein levels during interleukin-6 blockade. This case illustrates the diagnostic difficulty of childhood-onset recurrent inflammatory disease with atypical Still-like features that was ultimately recognized as systemic PAN in adulthood. Occult or under-recognized medium-vessel vasculitis may have been present earlier in the disease course. Long-term diagnostic reappraisal, vascular imaging when indicated, and continued follow-up across paediatric and adult rheumatology care may therefore be important in similar patients, particularly in the current biologic era.