Tubal otorrhea due to middle ear infection: The patient's recent ear tube placement and ongoing symptoms of otorrhea, despite being on oxygen for a cold, suggest a bacterial infection of the middle ear as the most likely cause. The presence of a cold could exacerbate or contribute to the development of this infection.

Chronic suppurative otitis media: Given the patient's history of ear tube placement and persistent otorrhea, chronic suppurative otitis media is a plausible diagnosis. This condition is characterized by a chronic infection of the middle ear and mastoid cavity.
Eustachian tube dysfunction: The patient's symptoms, including pulsating tinnitus and otorrhea after ear tube placement, could be related to Eustachian tube dysfunction, which might be exacerbated by the cold and underlying conditions like diabetes and CKD.
Biofilm formation on the tympanostomy tube: Biofilms can form on ear tubes, leading to persistent infection and otorrhea. This is a common issue in patients with ear tubes, especially if the tubes are not properly cleaned or if there is an underlying condition predisposing to infection.

Malignant otitis externa: Although less common, malignant otitis externa is a serious infection that can occur in diabetic patients and those with compromised immune systems. It requires prompt diagnosis and treatment to prevent severe complications.
Petrous apicitis: This is a rare but serious complication of otitis media that can occur in patients with diabetes or immunocompromised states. It involves infection of the petrous part of the temporal bone and can lead to severe neurological complications if not promptly treated.
Necrotizing otitis media: A severe form of otitis media that can lead to destruction of the temporal bone and surrounding structures. It is more common in diabetic patients and requires aggressive treatment.

Relapsing polychondritis: An autoimmune disorder that can cause inflammation of the cartilage in the ear, leading to otorrhea and other symptoms. It is rare but should be considered in patients with persistent symptoms that do not respond to typical treatments.
Granulomatosis with polyangiitis (GPA): A form of vasculitis that can affect the ears, among other areas, and cause symptoms like otorrhea and hearing loss. It is rare and typically presents with a combination of respiratory and renal symptoms.
Tuberculosis otitis media: Although rare in many parts of the world, tuberculosis can infect the middle ear, causing chronic otorrhea and other symptoms. It should be considered in patients who have been exposed to TB or have risk factors for the disease.