Xanthonychia Due to Staining From Carbidopa-Levodopa

Case Presentation

An 84-year-old female with a history of Parkinson disease presented with yellow discoloration of her fingernails for a few months. She had been taking carbidopa-levodopa for her Parkinson disease for many years, crushing the tablets into smaller pieces before ingesting. Physical examination was significant for a contracted left hand, xanthonychia of all 10 fingernails, and crumbling of the left fingernails (Figure 1). A clipping of the fingernails was performed to rule out onychomycosis and psoriasis as etiologies.

Figure 1.

Xanthonychia of fingernails due to staining from carbidopa-levodopa.

Teaching Point

In this case, the yellow nail discoloration was due to exogenous pigment from crushing and handling of her carbidopalevodopa medication. The yellow dye from the pill mixes with saliva and drips onto the patient’s fingernails, which was demonstrated to the authors during the clinic visit. The differential diagnosis for yellow discoloration of the nails includes onychomycosis, nail psoriasis, nail lichen planus, and yellow nail syndrome [1]. Our case stresses the importance of considering exogenous causes in diagnosing xanthonychia. The carbidopa-levodopa pills our patient was prescribed contain D&C yellow no. 10 aluminum lake, which give the pills a yellow appearance and has been previously associated with maculopapular rashes of the trunk and arms [2]. As carbidopa-levodopa can cause xanthonychia, patients should be counseled to wear gloves if they are chewing and handling the medication.