What are the pathophysiology and recommended treatment for pembrolizumab (Keytruda)-induced diabetes?

Pembrolizumab-Induced Diabetes: Pathophysiology and Treatment

Direct Answer

Pembrolizumab-induced diabetes is an autoimmune type 1 diabetes mellitus caused by PD-1 blockade triggering CD8 T cell-mediated destruction of pancreatic beta cells, and it requires immediate permanent insulin therapy—steroids do not prevent or reverse beta cell loss and should not be used for this purpose. 1

Pathophysiology

The PD-1/PD-L1 pathway normally protects pancreatic beta cells from autoimmune destruction. When pembrolizumab blocks PD-1, it removes this protective brake, allowing CD8 T cells to attack and destroy insulin-producing beta cells 1. This results in:

• Rapid onset of absolute insulin deficiency (often within days to weeks)
• Irreversible beta cell destruction
• Frequent presentation with diabetic ketoacidosis (DKA) as the initial manifestation 1, 2, 3

The incidence is low (<1% of patients), but appears more common with PD-1/PD-L1 inhibitors than with CTLA-4 inhibitors, and may be higher in patients previously treated with ipilimumab 1, 4.

Clinical Presentation

Patients typically present with:

• Acute hyperglycemia with DKA (most common presentation in 4/6 cases reviewed) 4
• Classic symptoms: polyuria, polydipsia, fatigue, nausea, abdominal pain 2, 3
• Rapid progression over days, not the gradual onset seen in typical type 1 diabetes
• Average age of onset: 58 years (range 42-77 years) 4, 5
• No sex predilection 4

Diagnostic Workup

Essential laboratory tests to confirm diagnosis and distinguish from type 2 diabetes: 1

1. C-peptide level (expect very low or undetectable, indicating absolute insulin deficiency) 2, 6
2. Anti-GAD (glutamic acid decarboxylase) antibodies
3. Anti-islet cell antibodies (ICA)
4. Anti-IA2 antibodies 2
5. HbA1c (often elevated, reflecting recent hyperglycemia)
6. Blood glucose monitoring should be performed regularly during pembrolizumab therapy to detect early hyperglycemia 1, 4

Note: Antibodies may be negative in pembrolizumab-induced diabetes despite clear autoimmune etiology 6, so low C-peptide with acute presentation is sufficient for diagnosis.

Treatment Algorithm

Acute Phase (DKA or Severe Hyperglycemia)

1. Treat DKA according to standard institutional protocols 1, 2, 3

   • IV fluid resuscitation
   • IV insulin infusion
   • Electrolyte correction
   • Monitor for complications

2. Do NOT use high-dose corticosteroids 1, 7

   • Critical point: Unlike other immune-related adverse events, steroids do NOT prevent or reverse beta cell destruction in pembrolizumab-induced diabetes 1, 7
   • Steroids will worsen glycemic control 1
   • A systematic review of 12 cases confirmed that ICI-induced type 1 diabetes cannot be reversed by steroids 7

Transition Phase

1. Transition to subcutaneous basal-bolus insulin regimen once DKA resolves 2, 3, 5
   • This is permanent therapy—beta cell function does not recover 7
   • Expect challenging glycemic control with alternating hyper- and hypoglycemia initially 6

Pembrolizumab Management Decision

1. Temporarily hold pembrolizumab during acute metabolic crisis 1, 2

2. Resumption of pembrolizumab after glycemic stabilization 1, 2, 8, 9

   • Once insulin therapy is established and glucose is controlled, pembrolizumab may be restarted 1
   • Multiple case reports document successful continuation of immunotherapy after diabetes stabilization 2, 8, 9
   • The oncologic benefit often outweighs the manageable endocrine toxicity
   • Decision should involve oncology and endocrinology collaboration 8

Key Clinical Pitfalls

• Do not delay insulin therapy waiting for antibody results—treat based on clinical presentation and C-peptide
• Do not use steroids as you would for other immune-related adverse events; they are ineffective and harmful here 1, 7
• Do not assume diabetes will resolve—this requires lifelong insulin, unlike some other pembrolizumab-related endocrinopathies 7
• Monitor glucose regularly during pembrolizumab therapy, especially in patients with prior ipilimumab exposure 4
• Recognize that presentation is often fulminant DKA, not gradual hyperglycemia—have high clinical suspicion 2, 3, 5

Long-term Management

• Permanent multiple daily insulin injections (basal-bolus regimen) 7, 2
• Standard diabetes education and monitoring
• Endocrinology follow-up for insulin dose optimization 6
• Continued oncologic therapy is feasible once metabolic control achieved 8, 9