Why do dialysis patients experience skin itch?

Causes of Skin Itching in Dialysis Patients

Uremic pruritus affects approximately 40-60% of hemodialysis patients and is caused by a combination of factors including uremic toxin accumulation, inflammation, xerosis, and secondary hyperparathyroidism. 1, 2

Pathophysiological Mechanisms

Primary Factors

• Inadequate dialysis clearance: Pruritus is more common in underdialysed patients, with studies showing improved symptoms when dialysis dose is increased to achieve a target Kt/V of approximately 1.6 1, 2
• Inflammation: Elevated C-reactive protein (CRP) levels positively correlate with the incidence and severity of uremic pruritus 1, 3
• Xerosis (dry skin): The most common cutaneous manifestation in dialysis patients, which may lower the threshold for itch even if not the primary cause 1

Secondary Contributors

• Calcium-phosphate imbalance: Abnormal mineral metabolism and secondary hyperparathyroidism 1, 2
• Anemia: May contribute to pruritus symptoms, with correction using erythropoietin potentially providing relief 1, 2
• Dialysis modality: Peritoneal dialysis generally results in lower severity of pruritus compared to hemodialysis 1
• Environmental factors: Rural residents may have higher risk of moderate itching compared to urban residents 3

Clinical Characteristics

• Distribution: In two-thirds of patients, pruritus is generalized; in others, it primarily affects the back, face, or arteriovenous fistula arm 1
• Timing: Often worse during summer or at night 1
• Onset: May begin within 6 months of starting dialysis, though some experience improvement initially 1
• Severity spectrum: Ranges from mild intermittent irritation to intractable itch that significantly impairs sleep and quality of life 1, 4

Impact on Outcomes

• Severe pruritus is associated with:
  • Diminished sleep quality 4
  • Reduced quality of life 5
  • Increased mortality rates in chronic hemodialysis patients 5, 4

Clinical Pearls and Pitfalls

• Prevalence variation: Uremic pruritus affects 40-90% of dialysis patients, with the most recent large studies suggesting approximately 42% in hemodialysis patients 1, 5
• Underdiagnosis: Despite its high prevalence, uremic pruritus is frequently underdiagnosed and undertreated 4
• Non-dialysis CKD: Pruritus can also occur in non-dialysis patients with stage 3-5 CKD, with increasing prevalence as kidney function worsens 4
• Dialysis quality: Higher dialysis efficacy (as measured by Kt/V) may reduce the prevalence of pruritus 6, 7
• Lack of biochemical markers: Individual laboratory values (hemoglobin, creatinine, urea, phosphorus, calcium, albumin, parathormone, alkaline phosphatase) may not reliably predict which patients will develop pruritus 6

Understanding these mechanisms is essential for developing effective treatment strategies, which should focus on optimizing dialysis adequacy, managing xerosis with emollients, normalizing calcium-phosphate balance, controlling PTH levels, and considering pharmacological interventions such as gabapentin when necessary.