AIDS-Related Opportunistic Infections, Abdominal Pain, Adult, Biopsy, CD4 Lymphocyte Count, Deglutition Disorders, Diagnosis, Differential, Duodenum, Dyspnea, Endoscopy, Gastrointestinal, Gastrointestinal Neoplasms, HIV Infections, Humans, Male, Sarcoma, Kaposi, Skin, Stomach