Yes, hydroxyurea can cause nail discoloration
Hydroxyurea is a well-documented cause of nail discoloration, most commonly presenting as melanonychia (nail hyperpigmentation) with longitudinal bands, transverse bands, or diffuse darkening of the nail plate. This is explicitly recognized in FDA labeling and multiple clinical guidelines 1.
Clinical Presentation
The nail changes from hydroxyurea typically manifest as:
- Longitudinal melanonychia (most common pattern) - dark vertical bands running the length of the nail 2
- Diffuse melanonychia - overall darkening of the entire nail plate 3
- Transverse bands - horizontal lines across the nail 3
- Blue-grey discoloration - particularly noted in polydactylic (multiple nail) involvement 4, 5
The discoloration can affect one nail or all 20 nails, with onset typically occurring 6-24 months after starting therapy 2. In one notable case, a patient developed bluish-grey longitudinal bands on all 20 nails within just 7 weeks of treatment 5.
Mechanism and Associated Features
The hyperpigmentation occurs through melanocyte activation induced by hydroxyurea 6. This is part of a broader spectrum of mucocutaneous toxicities listed in FDA labeling, which includes:
- Skin hyperpigmentation (particularly hands and feet)
- Nail dystrophy (onychodystrophy)
- Violet erythema
- Scaling of hands and feet
- Severe generalized hyperpigmentation 1
Clinical Management
The decision to continue or discontinue hydroxyurea depends on the severity of symptoms and the underlying indication for treatment 7, 8, 7:
When to Continue Treatment:
- Mild cosmetic changes without functional impairment
- Well-controlled underlying disease (e.g., polycythemia vera, essential thrombocythemia)
- Patient acceptance of the side effect 6, 5
When to Consider Discontinuation:
According to European LeukemiaNet and NCCN guidelines, hydroxyurea should be discontinued for "unacceptable mucocutaneous manifestations" 7, 8, 7. This includes:
- Leg ulcers
- Severe cutaneous vasculitic toxicities
- Vasculitic ulcerations and gangrene 1
Important caveat: Simple nail discoloration alone, while cosmetically concerning, does not typically meet criteria for drug discontinuation if the underlying hematologic condition is well-controlled. The guidelines specifically mention leg ulcers and severe mucocutaneous manifestations as reasons to stop, but melanonychia is generally considered a manageable side effect 7.
Differential Diagnosis Considerations
When evaluating nail discoloration in a patient on hydroxyurea, consider that the British Association of Dermatologists guidelines note that bacterial infections (particularly Pseudomonas aeruginosa) can cause green or black nail discoloration 9. However, hydroxyurea-induced changes are typically:
- Bilateral and symmetric when multiple nails are involved
- Associated with other skin hyperpigmentation
- Temporally related to drug initiation
- Not associated with nail softening or friability (unlike fungal infections) 9
Patient Counseling
Inform patients that:
- Nail discoloration is a recognized side effect that may develop months after starting treatment
- The changes are generally reversible after drug discontinuation, though this may take considerable time
- The discoloration does not indicate treatment failure or disease progression
- Continuation of therapy should be based on the balance between disease control and tolerability 5
The FDA labeling explicitly lists "nail abnormalities" among dermatologic reactions, and acute mucocutaneous toxicity with severe hyperpigmentation is documented in overdose scenarios 1.