Hypotheses
The 2 most likely diagnoses are:
- psoriasis causing nail changes while psoriatic arthritis is developing
- onychomycosis with incidental joint pain of the DIP joint.
Other causes of nail changes include lichen planus, chronic candida paronychia, and Reiter’s disease. Epidemiologically the most likely diagnosis is onychomycosis, which is far more prevalent than the other conditions. However, this patient has already failed a course of an oral antifungal agent, and her nail changes are more consistent with psoriasis.
Hypothesis testing
Questions and physical examination focus on collecting data to determine the more likely of the two diagnoses, psoriasis and fungal nail disease. The patient denied having any skin lesions and a history of psoriasis. She also said she had no athlete’s foot or problems with her toenails or other hand. Her knees ache from time to time, which she attributed to aging.
Physical exam revealed no evidence of psoriasis on the skin and no tinea pedis or onychomycosis of the toenails. She had no other skin findings suggestive of lichen planus or Reiter’s disease. Looking more closely at the fingernails, we saw no evidence of subungual keratoses, which are frequently found in onychomycosis.
A scraping and clipping of the fingernail was sent for fungal culture, and an x-ray film of that digit revealed no bony changes. The fungal culture results 2 weeks later were negative.
Patient follow-up
We made a presumptive diagnosis of psoriatic nail changes and psoriatic arthritis, and the patient was sent to a rheumatologist for consultation. The rheumatologist agreed with the diagnosis and placed the patient on nonsteroidal anti-inflammatory drugs to treat the early psoriatic arthritis.
The patient developed more areas of psoriatic arthritis involvement over the subsequent years and became less concerned about the appearance of her nails. Eventually the psoriatic arthritis progressed to the point where the patient was taking remititive agents for inflammatory arthropathy. She never did develop the skin lesions of psoriasis.
Nail changes of psoriasis
It has been reported that 30% of patients with psoriasis have nail changes, the most common being pitting. Onycholysis is the next most frequent change, and the oil spot is less frequent but not rare.
Not everyone with nail pitting has psoriasis; however, there is a high correlation between psoriatic arthritis and nail pitting.
Patients with psoriasis and psoriatic arthritis have a higher percentage of nail changes than patients with psoriasis of the skin only. In 1 study, nail changes were noted in 86.5% of patients affected by arthropathic psoriasis, and the most common fingernail change was pitting.2