Visceral leishmaniasis (VL) is a neglected vector-borne disease caused by obligate intracellular protozoa of the genus Leishmania. In immunocompromised patients, VL may present atypically, progress more aggressively, and respond less favorably to treatment. We present the case of a 62-year-old male with chronic inflammatory demyelinating polyneuropathy (CIDP) receiving long-term corticosteroids and azathioprine who developed relapsing VL complicated by post-kala-azar dermal leishmaniasis (PKDL). The patient initially presented with prolonged fever, pancytopenia, hepatosplenomegaly, and weight loss. Bone marrow aspirate revealed Leishmania amastigotes. Intravenous lyposomal amphotericin B (L-AMB) achieved temporary remission; however, PKDL and VL recurred one year later. Despite receiving sequential therapy with L-AMB and miltefosine, the patient experienced further relapses, likely due to severe T- and B-cell lymphopenia and marasmic-like malnutrition. VL should be considered in the differential diagnosis of prolonged fever and cytopenias in immunosuppressed patients in Mediterranean Europe, even in the absence of travel history. Chronic immunosuppression, secondary immunodeficiency, and malnutrition can significantly impair treatment response and favor recurrence, highlighting the need for integrated clinical, nutritional, and epidemiological management strategies.