Muehrcke Lines of the Fingernails

Etiology

Several conditions may trigger the hypoalbuminemia implicated in Muehrcke's nails. Nephrotic syndrome, glomerulonephritis, liver diseases, and malnutrition are the most common, with nephrotic syndrome being the most common cause reported by Muehrcke. Other cases include periods of high metabolic stress (e.g., systemic inflections, AIDS). Trauma may also cause Muehrcke's nails. Chemotherapy is another documented etiology. Mountain climbers may also experience this phenomenon.

Epidemiology

The incidence of Muehrcke’s nails is uncertain. The literature espouses it is a rare condition. A literature review of PubMed using the terms “Muehrcke”/“Muehrcke’s” independently or with “lines”/“nails” resulted in a mere 27 publications. However, it may be underreported given its association with underlying systemic disorders for which patients may be treated by medical providers who may not be aware of this clinical finding. Although some reports involve children, the vast majority reference adult patients.[4]

Pathophysiology

Typically, Muehrcke's nails are the result of hypoalbuminemia. Although the exact pathophysiology is unclear, it is thought that a localized edematous state in the nailbed results in increased pressure on the vasculature in this region. As a result, the normal appearance of erythema observed through the nail plate is not seen. Instead, a Muehrcke's nail/line is seen. This theory is corroborated by an array of studies documenting this finding in patients with hypoalbuminemia, ranging from <2.2 g/100 mL as in Muehrcke's original study up to 2.7 g/100 mL.[1][5] 

Trauma may similarly result in local edema or damage to the nail bed and associated vasculature, limiting visible erythema. In extreme elevations, physiologic changes to blood circulation may predispose to Muehrcke's nails. What is less understood, however, is how systemic chemotherapy induces Muehrcke's nails as reports in this patient population document higher (e.g.,>3.4 g/100 mL) and even normal albumin levels.[3][6][7] It is known that nail changes, including pigmentation changes and dystrophy, can occur with chemotherapy.[3][8] These may also more often be transverse bands of pigment. These may not be true cases of Muehrcke's nails as associated with hypoalbuminemia, as originally reported by Muehrcke.

Histopathology

Few papers comment on histopathologic findings in Muehrcke’s nails. James and Odom observed this finding in a patient of theirs undergoing treatment with cyclophosphamide, doxorubicin hydrochloride, and vincristine sulfate. They hypothesized that the chemotherapeutic agents would affect the nail matrix, causing parakeratosis, and dyskeratosis would be retained into the nail plate. However, they did not observe these findings. Their repeat biopsies of the white bands showed no consistent findings.[7] 

Somewhat similarly, Nabai personally observed his own nail changes during his heart transplantation and after. He noted that the histological section of his nail plates demonstrated orthokeratotic keratinous material and areas suggestive of delayed keratinization. There was no definite appearance of parakeratosis, distortion, or thinning of the nail plates.[6] Larger cohort studies, including Muehrcke’s, do not comment on histopathologic findings.[1]

History and Physical

As the possible causes of Muehrcke’s nails grow, a complete and detailed history is important to elicit an etiology. Questions about patients’ underlying medical conditions, exposures, medication, and occupation should be included. The chronology of nail findings in relation to history should be understood. A review of systems should also be probed, although this condition is typically benign.[9] However, treatment with systemic anticancer drugs (particularly taxanes or EGFR inhibitors) may result in nail changes, pain, and functional impairments.[10]

On physical examination, the transverse white bands run parallel to the lunula and are separated by areas of normal pink nailbed color. These white bands are only different in color and have no other palpable difference compared to the rest of the nail. Muehrcke’s nails are often present on the second, third, and fourth fingernails, whereas the thumbnail is rarely involved. The white lines disappear with pressure (hence the term ‘apparent’ leukonychia).[1] Associated melanonychia may also be present in patients undergoing chemotherapy.[11]

Evaluation

The history and physical examination provide the backbone for the diagnosis of this condition. Since this condition represents underlying pathophysiology involving the nail bed's vasculature, a biopsy is not recommended. Laboratory tests should be obtained as guided by patient history. Even though the number of possible etiologies continues to grow, the most important and commonly obtained test is likely serum albumin levels (levels <2.2 g/100 mL are most often associated). Other measures assessing for malnutrition could be considered, including total serum protein, serum chemistries, complete blood count, and urinalysis. For patients undergoing chemotherapy, blood levels of the therapeutic agent used can be obtained to assess for toxicity. Imaging studies are not needed.

Treatment / Management

Treatment is case-specific. In cases of Muehrcke's nails secondary to hypoalbuminemia, treatment with serum albumin infusions can result in a resolution. Treatment should be given until levels are in the normal range. However, it is important to note that treating the underlying conditions that may be the etiology aids in correcting the normal albumin levels. Some reports have shown effective fading of these lines by adding cortisone and/or corticotropin therapy to albumin infusions.[1]

Differential Diagnosis

The most pertinent clinical conditions on the differential diagnosis for Muehrcke's nails are Beau's lines, Mees' lines, and Terry's nails. Beau's lines are perceptible and palpable deep grooved ridges running side-to-side on the fingernail or toenail secondary to a temporary delay in nail division in the nail matrix (e.g., infection, trauma).[12] Mees' lines (also known as Aldrich or Reynolds' lines) are white, non-blanching (an important distinguishing feature from Muehrcke's nails), transverse bands running parallel to the lunula secondary to an insult to the distal nail matrix causing parakeratosis of the ventral nail plate. They are often associated with arsenic poisoning, other metal toxicity, congestive heart failure, and some infections.[13] 

In Terry's nails, most of the nail plate turns white (the lunula is obliterated) with a characteristic ground glass appearance secondary to a decrease in vascularity and an increase in connective tissue in the nail bed. They were originally associated with cirrhosis, but have now been documented in up to 25% of hospitalized patients in general.[14][15]

Prognosis

As a clinical finding, Muehrcke's nails themselves do not lend prognostic value. The prognosis of the patient hinges on the underlying condition that leads to this finding. As noted by Muehrcke, treatment of the underlying condition (e.g., hypoalbuminemia) can often result in the lines' disappearance.[1]

Complications

Muehrcke’s nails do not result in complications but are instead a complication of an underlying systemic condition. However, it is important to know that in the case of chemotherapy or trauma as the etiology of Muehrcke’s nails, patients may have pain and some functional limitation, which may contribute to morbidity. Patients with malignancies necessitating chemotherapy may be sick and limited functionality, so addressing functionality concerns and pain related to Muehrcke’s nails is important. Some patients may also be concerned about the cosmetic appearance of their nails. For these patients, it is important to understand the psychosocial ramifications of how this condition may bother them and form a strong partnership to address these concerns by treating the underlying condition.