Eosinophilic granulomatosis with polyangiitis presenting with eosinophilic myositis: A case report and review of literature

Dear Editor, A 59-year-old Japanese male had noticed muscle weakness over his legs 1 month previously and eruptions on his legs 1 week previously. He had asthma and allergic rhinitis since childhood and no history of nasal polyps. He had no medication previously. Physical examination revealed no other organ symptoms but purpura with mild induration of the lower extremities [Figure 1a and b] and peripheral neuropathy from both knees to the toes. Manual muscle test revealed bilateral muscle weakness with a right-sided predominance: 1/2 tibialis anterior, 1/2 triceps surae, 2/3 iliopsoas, 3/3 quadriceps, and 3/3 flexor femoris. Blood tests showed increased eosinophil counts (22,396/μL), creatine kinase (CK; 1257 U/L), and aldolase (18.9 IU/L). Other autoantibodies were not detected by enzyme-linked immunosorbent assay, including antineutrophil cytoplasmic antibody (ANCA). Computed tomography showed an overall thickening of the bronchial wall, a finding of bronchial asthma. Soft shadows in ethmoid and maxillary sinuses and thickening of the nasal mucosa were also present, with findings of sinusitis. A biopsy specimen from a purpura on his left leg showed perivascular infiltration of eosinophils and fibrinoid necrosis in the blood vessel walls of the superficial dermis [Figure 1c and d]. Direct immunofluorescence demonstrated C3 deposition on the vessels in the dermis [Figure 1e]. Magnetic resonance imaging showed myositis in his quadriceps [Figure 1f]. Electromyography showed deinnervation findings with decreased mobilization of motor unit potentials and attenuated interference patterns in the right tibialis anterior muscle. Evoked electromyography did not elicit action potentials in the nerves of the lower extremities, suggesting severe peripheral neuropathy. A quadriceps muscle biopsy showed fibrinoid necrosis and nuclear debris around the blood vessels, with infiltration of eosinophils and mononuclear cells, indicating myositis with eosinophil infiltration [Figure 1g and h]. There were no findings of leukemia, parasitic infection, or other organ involvement. According to the 2022 American College of Rheumatology/European Alliance of Associations classification criteria, the score was 11; maximum eosinophil count ≥1 × 109/L (+5), obstructive airway disease (+3), extravascular eosinophilic predominant inflammation (+2), and mononeuritis multiplex/motor neuropathy not due to radiculopathy (+1).[1] We diagnosed him with eosinophilic granulomatosis with polyangiitis (EGPA) with eosinophilic myositis. Hypereosinophilic syndrome was denied by the EGPA diagnosis. We treated him with corticosteroid pulse therapy (1000 mg/day, 3 days), prednisolone (60 mg/day), and mepolizumab (300 mg, 4 weeks) to control disease activity and intravenous immunoglobulin (400 mg/kg/day, 5 days, 2 times) for his peripheral neuropathy. In the blood tests, eosinophil count, C-reactive protein, and CK returned to within normal ranges on day 3 of steroid pulse. After ~2 weeks, the disease activity score, Birmingham Vasculitis Activity Score, decreased from 16 to 7. His eruptions and myositis were cured; however, peripheral neuropathy partially remained.Figure 1: (a and b) Physical examination at the first visit. (c and d) Histopathological findings of the cutaneous biopsy specimen from a purpura on his left leg (H and E staining; ×40 [c] and × 400 [d]). (e) Direct immunofluorescence with C3 deposition in superficial dermal vessels. (f) Magnetic resonance imaging showing myositis in his quadriceps. (g and h) A quadriceps muscle biopsy (H and E staining; ×40 [g] and × 400 [h]).Although myositis is a complication of various autoimmune diseases, it is relatively rare in EGPA. We summarized the clinical data of the 11 EGPA cases, including our case,[2-5] whose myositis was confirmed by muscle biopsy. We compared these data to previous surveys of EGPA in Japan[6] and worldwide[7] [Supplementary Table 1]. Patients with EGPA with myositis were older than those with usual EGPA, which might be owed to a selection bias. We tend to perform muscle biopsies for older patients who easily have difficulty walking because of their potentially decreased muscle function. Supplementary Table 1 also shows some differences in the average eosinophil counts and organ involvement in the eyes/nose/throat and a positive rate of ANCA. Although the number of cases is small, no gastrointestinal or renal involvement has been reported in cases complicated by myositis. A study investigating the difference in the prevalence of organ involvement in EGPA between ANCA-positive and-negative cases has been reported,[8] but it does not include information on myositis. Although the number of cases is limited, based on our compiled results, the ANCA-positive rate seems more common in EPGA patients with myositis.Neuropathy in usual EGPA often occurs with movement disorders and numbing pain, which could mask myositis symptoms. According to Supplementary Table 1, we should be careful not to miss the signs of myositis when assessing muscle strength, muscle pain, and elevated levels of serum CK, especially in older patients with EGPA. The presence of myositis should be most appropriately evaluated at the start of EGPA treatment, but it should also be kept in mind in the presence of elevated CK, muscle weakness, muscle pain, and as a differential for suspected steroid myopathy. It is important to assess the condition of the muscles early, either before initiating treatment or shortly after treatment initiation, to evaluate the disease status more accurately. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for his images and other clinical information to be reported in the journal. The patient understands that his name and initials will not be published and due efforts will be made to conceal his identity, but anonymity cannot be guaranteed. Data availability statement The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.