What is the likely diagnosis for an elderly male with a history of Benign Prostatic Hyperplasia (BPH), presenting with polyuria, nocturia, blurred vision, polyphagia, and polydipsia, and having a non-fasting glucose level indicating hyperglycemia?

Diagnosis: New-Onset Type 2 Diabetes Mellitus

This patient has new-onset type 2 diabetes mellitus, not a primary BPH exacerbation. The constellation of polyuria, polydipsia, polyphagia, and blurred vision with a non-fasting glucose of 180 mg/dL represents the classic hyperglycemic syndrome, and diabetes must be diagnosed and treated immediately 1, 2.

Primary Diagnostic Reasoning

The urinary symptoms are secondary to osmotic diuresis from glucosuria, not BPH progression. While this patient has a history of BPH, the acute onset of symptoms "a few months ago" combined with the classic triad of polyuria, polydipsia, and polyphagia points definitively to diabetes mellitus as the primary pathology 1. Diabetes causes polyuria through glucose spilling into urine and creating osmotic diuresis, which is mechanistically distinct from BPH-related obstructive symptoms 3.

Key Distinguishing Features

• Classic hyperglycemic symptoms are present: The combination of polyuria, polydipsia, polyphagia, and blurred vision represents marked hyperglycemia 1
• Non-fasting glucose of 180 mg/dL is diagnostic when symptoms are present: A random plasma glucose ≥200 mg/dL with classic symptoms is sufficient for diagnosis without additional testing, but this patient's 180 mg/dL requires confirmatory testing 2
• Blurred vision indicates hyperglycemic complications: This symptom reflects osmotic changes in the lens from sustained hyperglycemia and is not explained by BPH 1

Required Confirmatory Testing

Order an HbA1c immediately as the single most practical confirmatory test 4. The American Diabetes Association recommends confirming diabetes with repeat testing when a single glucose measurement is elevated but the patient lacks unequivocal hyperglycemia (defined as random glucose ≥200 mg/dL) 4, 2.

Diagnostic Thresholds for Confirmation

• HbA1c ≥6.5% (48 mmol/mol): Confirms diabetes mellitus; initiate treatment immediately 4
• HbA1c 5.7-6.4% (39-47 mmol/mol): Indicates prediabetes; initiate intensive lifestyle modification 4
• HbA1c <5.7% (<39 mmol/mol): Further evaluation needed, though unlikely given the clinical presentation 4

Alternatively, a fasting plasma glucose ≥126 mg/dL or 2-hour oral glucose tolerance test ≥200 mg/dL would also confirm the diagnosis 4.

Why This Is NOT Diabetes Insipidus

The elevated blood glucose immediately rules out diabetes insipidus 3. Diabetes insipidus requires normal glucose levels and is characterized by the inability to concentrate urine due to ADH deficiency or resistance, not osmotic diuresis from glucose 3. The diagnostic triad for diabetes insipidus includes urine osmolality <200 mOsm/kg with high-normal or elevated serum sodium, which is incompatible with diabetes mellitus 3.

Relationship Between Diabetes and BPH

Diabetes and hyperglycemia independently worsen BPH symptoms and increase the risk of BPH progression 5, 6, 7, 8. However, in this acute presentation, the urinary symptoms are primarily driven by osmotic diuresis from uncontrolled diabetes, not BPH exacerbation 1, 3.

Evidence Supporting This Relationship

• Diabetic patients have significantly higher International Prostate Symptom Scores (IPSS) and larger prostate volumes compared to non-diabetic patients 6, 7
• HbA1c levels ≥6.5% are associated with worse IPSS scores and lower maximum urinary flow rates 7
• Hyperglycemia and insulin resistance increase the risk of BPH progression in elderly patients with type 2 diabetes 7, 8
• The stable PSA of 1.2 suggests no acute prostatic pathology 9

Critical Next Steps

Initiate diabetes treatment immediately after diagnostic confirmation 4, 2. Delaying treatment can lead to progression to diabetic ketoacidosis and other acute complications 2.

Expected Clinical Course

• Urinary symptoms should improve significantly with glycemic control: Once blood glucose normalizes, the osmotic diuresis will resolve, and polyuria/nocturia should decrease substantially 1
• If urinary symptoms persist after glycemic control, then address BPH: Consider alpha-adrenergic blockers or 5-alpha reductase inhibitors for persistent BPH symptoms 9
• Managing hyperglycemia may slow BPH progression: Achieving good glycemic control and weight management can reduce the risk of BPH worsening over time 7

Problem Statement Refinement

Your problem statement should emphasize diabetes mellitus as the primary diagnosis: "An elderly male with a history of BPH presenting with new-onset polyuria (6-7 times per day), nocturia (3-4 times per night), polydipsia, polyphagia, and blurred vision over the past few months. Non-fasting glucose is 180 mg/dL with stable PSA at 1.2. Clinical presentation is consistent with new-onset type 2 diabetes mellitus with secondary osmotic diuresis contributing to urinary symptoms."