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Dermoscopy
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Dx: Green nail syndrome caused by Pseudomonas aeruginosa
This patient had green nail syndrome (GNS), an infection of the nail bed caused by Pseudomonas aeruginosa. These bacteria produce pyocyanin, a blue-green pigment that discolors the nail.1 GNS often occurs in patients with prior nail problems, such as onychomycosis, onycholysis, trauma, chronic paronychia, or psoriasis.
Nail disease disrupts the integumentary barrier and allows a portal of entry for bacteria. Scanning electron microscopy of patients with GNS has shown that fungal infections create tunnel-like structures in the nail keratin, and P aeruginosa grows in these spaces.2 Nails with prior nail disease that are chronically exposed to moisture are at greatest risk of developing GNS,3,4 and it is typical for only one nail to be involved.5Pseudomonas is the most common bacterial infection of the nails, but is not well known because it is rarely reported and patients often don’t seek care.6
In our patient’s case, her prior onychomycosis helped to create a favorable environment for the growth of the bacteria. Onycholysis—characterized by separation of the nail plate from the nail bed—was also present in our patient, based on her description of a “spongy” nail bed and loose nail, allowing moisture and bacteria to infiltrate the space. Onycholysis is associated with hypothyroidism, which the patient also had.7 The frequent soaking of her hands during dishwashing and bathing her children helped to provide the moist environment in which Pseudomonas thrives.
As was the case in this patient, GNS is often painless, or may be accompanied by mild tenderness of the nail. Patients may seek treatment primarily for cosmetic reasons.
GNS can be diagnosed by clinical observation and characteristic pigmentation along with an appropriate patient history.4 Culture of the nail bed may be helpful if bacterial resistance or co-infection with fungal organisms is suspected.
Changes in nail color can be a sign of many conditions
Nail discoloration, or chromonychia, can present in a variety of colors. Nail findings may represent an isolated disease or provide an important clinical clue to other systemic diseases.8 The specific shade of discoloration helps to differentiate the underlying pathology.
Yellow nail syndrome. As the name implies, this syndrome typically causes yellow discoloration of the nail (although yellow-green is also possible). Yellow nail syndrome is believed to be due to microvascular permeability, which also accounts for its associated clinical triad: hypoalbuminemia, pleural effusion, and lymphedema. Yellow nail syndrome may be seen in patients with bronchiectasis, internal malignancies, immunodeficiency, and rheumatoid arthritis.8
Nail bed hematoma. Among the most common causes of nail discoloration, these lesions typically appear as reddish to reddish-black, depending on the age of the bleed, and will often have streaks at the distal margin of the lesion.9 Risk factors for hemorrhage include blood thinners and clotting disorders. Subungual hemorrhages that do not grow out with the nail, or that recur in the same place, may require biopsy.9
Subungual melanoma causes black-brown discoloration of the nails, and may form a longitudinal band in the nail.9 Longitudinal melanonychia is a common variant in African American individuals.10 Features that increase the likelihood of melanoma include a family history of melanoma, a sudden change in the appearance of the lesion, band width greater than 3 mm, pigment changes extending into the cuticle (known as Hutchinson’s sign), and nail plate disruption.
Dermoscopy, the technique of using surface microscopy to examine the skin, may be helpful in distinguishing nail lesions. (See a video on how to perform dermoscopy here: http://bit.ly/2pyJ3xN.)
Nonmelanocytic lesions tend to have homogeneously distributed pigment, while melanocytic lesions contain granules of pigment in cellular inclusions. Any suspicion of melanoma warrants a punch biopsy.11