Unusual 18F-FDG PET/CT Images in Pediatric Systemic Lupus Erythematosus

Background Systemic Lupus Erythematous (SLE) is a complex autoimmune disease that can affect multiple organs. Uncommon presentations may delay diagnosis and introduction of proper therapies. We report a case of SLE in 15-year-old girl with extensive fascia involvement detected by 18F-FDG PET/CT imaging. To our knowledge, this finding has not previously been reported in SLE.

Case Report We present the case of a 15-year-old Haitian girl with no significant past medical history who presented with a 6-month history of progressive fatigue, arthralgias and myalgias. Clinical examination was notable for polyarthritis, painful subcutaneous nodules on the upper and lower extremities, hemorrhagic bullous lesions on the toes and absence of muscle weakness. Investigations revealed bicytopenia (Hb 68 g/L; lymphocytes 0.8×10^9/L), elevated inflammatory markers (C protein reactive 45 mg/L and serum erythrocyte sedimentation rate 60 mm/h), low levels of complement C3 (0.39 g/L) and C4 (0.06 g/L), elevated serum immunoglobulin G (23.57 g/L), normal muscular enzyme levels (CK 68 U/L), proteinuria (urine protein/creatinine ratio 0.39 g/mmol) and mild microscopic hematuria. Autoantibodies tests were significantly positive for anti-nuclear (1/640 homogenous pattern), anti-double-stranded DNA (139.9 UI/mL, normal < 100 UI/mL) but negative for anti-extractable nuclear antigen. While awaiting specific autoantibody results, 18F-FDG PET/CT was performed to better understand the underlying process and help in the differential diagnoses. The study demonstrated increased FDG uptake/avidity in (a) fascias of bilateral upper and lower extremities (Figure 1), a feature that, to our knowledge, has not previously been reported in SLE; (b) the muscles predominantly in the upper limbs; (c) the basal ganglia; (d) both kidneys and (e) multiple lymph nodes. Renal biopsy revealed a diffuse segmental lupus nephritis (class IV-S). The patient was started on immunomodulatory therapy (intravenous steroids pulses, intravenous belimumab, mycophenolate mofetil and hydroxychloroquine), resulting in progressive symptoms resolution including relief from upper and lower limb pain, which were not only related to myositis but also to inflammatory fasciitis.

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Figure 1:

¹⁸F-FDG PET/CT demonstrated increased FDG uptake/avidity in fascias of bilateral upper and lower extremities

Conclusion This is the first SLE patient reported with extensive fascia uptake on 18F-FDG PET/CT. In patients with SLE, typical 18F-FDG PET/CT findings include cerebral metabolism modifications and increased metabolic activity in lymph nodes, the spleen and bone marrow.[1] This unique case highlights the importance of recognizing SLE in patients presenting with inflammatory fasciitis or when extensive fascia uptake is seen on 18F-FDG PET/CT.

References [1.] Curiel R. Ann N Y Acad Sci 2011;1228:71-80.