Anal fissure: A tear in the lining of the anus can cause itching, pain, and bleeding. The constant itching reported by the patient could be due to an anal fissure, especially if there's no visible external hemorrhoid.

Pruritus ani: A common condition characterized by intense itching around the anus, often without a clear cause. It could be due to poor hygiene, dietary factors, or skin conditions.
Internal hemorrhoids: Although external hemorrhoids are not visible, internal hemorrhoids could still be present and cause itching, especially if they prolapse or bleed.
Fungal or bacterial infections: Infections like candidiasis or bacterial dermatitis can cause anal itching and may not have visible external signs.

Inflammatory bowel disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause anal itching, among other symptoms. Missing these diagnoses could lead to delayed treatment and significant morbidity.
Anal cancer: Although rare, anal cancer can present with itching, pain, or bleeding. Early detection is crucial for effective treatment.
STDs (sexually transmitted diseases): Certain STDs, such as herpes or syphilis, can cause anal itching and may not have obvious external signs.

Lichen sclerosis: A rare skin condition that can cause itching, pain, and scarring in the anal area.
Leukoplakia: A condition characterized by white patches on the mucous membranes, which can cause itching and may be a precursor to cancer.
Paget's disease: A rare skin condition that can cause itching, pain, and bleeding in the anal area, often associated with underlying cancer.