A 23-year-old man presented to our department with cyanosis in both hands and a painful ulcer on the second and third fingers of his right hand, which had appeared 5 days prior. He also reported experiencing paresthesia in his toes and intermittent claudication in his lower limbs for the past 2 months.

There was no history of fever, respiratory symptoms, or oral or genital ulcers. Additionally, no history of autoimmune disease was found in his family history, and he had never smoked and denied any drug involvement.

During the physical examination, his body temperature was within the normal range, and his blood pressure was normal in both his upper and lower limbs, showing no noticeable difference. His distal fingers appeared cold and slightly cyanotic, with painful ulcers and infarction on the right hand's second and third fingers. The reduced capillary filling was observed in all fingers of his upper limbs. Peripheral pulse examination revealed intact ulnar and radial pulses, but the dorsalis pedis pulses were absent (Fig. 1).

The patient’s ischemic manifestations with digital infarctions. A Ischemic manifestations of both hands, gangrenous changes localized to the second and third fingers of the right hand. B Ischemic signs in the lower extremities with concomitant gangrenous changes specifically affecting the first toe of the left leg

There were no visible erythematous, angioedematous, urticarial lesions, pruritic papules, or nodules at the time of presentation. Other systemic examinations, including musculoskeletal, respiratory, ocular, cardiac, and abdominal evaluations, revealed no significant findings.

The complete blood count results revealed a total white blood cell count of 17.5 K/μL (normal range: 4–10), with an absolute eosinophil count of 4.9 K/μL (normal range: 0.01–0.8). Hemoglobin level was measured at 13.3 g/dL (normal range: 12–15), and the platelet count was 164 K/μL (normal range: 150–400). The C-reactive protein level and erythrocyte sedimentation rate were within normal ranges. Additionally, the levels of creatinine, liver function markers, and results of urinalysis and hsTroponin I did not show any abnormalities. Baseline prothrombin time and activated partial thromboplastin time were normal, although the D-dimer level was elevated. Comprehensive infection screening tests, including HIV, hepatitis B and C viruses, Strongyloides, and Toxocara, all returned negative results. Stool tests for ova and parasites were also negative.

Further immune serology screening was performed to explore potential underlying factors contributing to hypereosinophilia. The results indicated negative findings for p-ANCA, c-ANCA, anti-B2 glycoprotein, antinuclear antibody, anti-double-stranded DNA, lupus anticoagulant, rheumatoid factor, anti-phospholipid panel, and anticardiolipin. Levels of complement (C3, C4) and immunoglobulins were within normal ranges. Genetic testing was conducted to investigate possible heterogeneous causes, but no FIP1L1/PDGFRA gene fusion was detected. Immunophenotyping of T-cell and T-cell receptor rearrangement studies were not conducted due to limitations in genetic and laboratory testing in Vietnam.

A transthoracic echocardiogram revealed no signs of vegetations, valve involvement, or abnormalities in heart wall motion. Abdominal sonography yielded normal results. Electromyography indicated severe bilateral polyneuropathy in the lower limbs. However, lumbar and sacral spine MRI showed no evidence of spinal cord disease. Doppler ultrasonography identified arterial thrombosis affecting anterior and posterior tibialis arteries of both lower extremities, and these findings were confirmed by CT angiography (Fig. 2).

Extremity angiography on computed tomography. A Normal angiography of the upper limbs. B Occlusion of the anterior and posterior tibialis arteries without evidence of atherosclerosis

Skin biopsy was not conducted mainly because of apprehensions regarding ischemic-induced wound healing impairment in the gangrene lesion. The patient received aspirin and heparin treatment upon admission, so bone marrow biopsy was not indicated, primarily due to concern about the potential risk of significant hemorrhagic complications.

The most likely diagnosis of small and medium vessel vasculitis induced by hypereosinophilic syndrome (HES) was established. Although the subtype of HES could not be confirmed in this case, we decided to commence corticosteroid treatment, which is considered first-line therapy in most forms of HES. To initiate treatment. We used immunosuppressant therapy with methylprednisolone at a dosage of 1 mg/kg/day for 2 weeks. Additionally, anticoagulation treatment was continued using low molecular weight heparin. The patient was also prescribed aspirin at a daily dosage of 81 mg and atorvastatin at a daily dosage of 20 mg. This treatment regimen resulted in significant improvements both clinically and in laboratory parameters. The patient reported a noticeable reduction in digital pallor and improvement in intermittent claudication symptoms. Upon physical examination, the patient's distal pulses in the lower limbs were now detectable. The eosinophil level decreased from over 4.9 to 0.9 K/μL (Table 1). However, the lower-limb arterial Doppler scan performed at discharge indicated ischemia evidence with the image of monophasic flow and thrombosis in the anterior and posterior tibialis arteries of both legs (Fig. 3).

Doppler ultrasound of lower extremity’s vascular after 2 weeks of treatment. A Images of single-phase waveforms in the anterior and posterior tibialis arteries. B Thrombosis-induced partial occlusion of the tibialis arteries

Following 2 weeks of treatment during hospitalization, the patient was discharged and prescribed methylprednisolone at a daily dosage of 1 mg/kg/day. Additionally, the patient was scheduled for regular follow-up appointments at our outpatient clinic.