What is the cause of lower abdominal discomfort, bloating, and white vaginal discharge in a 47-year-old female with stage 4 small cell lung carcinoma (SCLC) and metastases to the bone and brain, currently on immunotherapy, who recently completed a course of Augmentin (amoxicillin-clavulanate) for bacterial sinusitis?

Differential Diagnosis for 47-year-old Female with Small Lung Cell Carcinoma

Single Most Likely Diagnosis

• Vaginal Yeast Infection: Given the patient's recent course of antibiotics (Augmentin) for bacterial sinusitis, she is at increased risk for a vaginal yeast infection, which is consistent with her symptoms of white vaginal discharge and lower abdominal discomfort.

Other Likely Diagnoses

• Urinary Tract Infection (UTI): Although the patient denies dysuria, urgency, or frequency, a UTI could still be present, especially given her concern about having a UTI and her history of chronic sinusitis, which may indicate a predisposition to infections.
• Bacterial Vaginosis: This condition could also explain the vaginal discharge and is a common cause of vaginal symptoms in women of reproductive age.
• Immunotherapy-related Side Effects: The patient is currently on immunotherapy, which can cause a range of side effects, including gastrointestinal symptoms like bloating and abdominal discomfort.

Do Not Miss Diagnoses

• Tumor Lysis Syndrome: Although less likely, given the patient's stage 4 small lung cell carcinoma, tumor lysis syndrome is a life-threatening condition that can occur, especially after chemotherapy or immunotherapy, and can cause abdominal discomfort among other symptoms.
• Spinal Cord Compression: Metastases to the bone can cause spinal cord compression, leading to abdominal discomfort, among other neurological symptoms. This is a medical emergency that requires prompt diagnosis and treatment.
• Brain Metastasis-related Symptoms: Given the patient's history of brain metastases, any new or worsening neurological symptoms, including those that might seem unrelated like abdominal discomfort, should be thoroughly evaluated to rule out progression of brain metastases.

Rare Diagnoses

• Ovarian Cancer: Although the patient has a known primary cancer, the possibility of a second primary cancer, such as ovarian cancer, should be considered, especially if the symptoms persist or worsen despite treatment for more likely causes.
• Gastrointestinal Metastases: Metastases to the gastrointestinal tract from small lung cell carcinoma are rare but could explain the patient's abdominal symptoms.