• View in gallery

    KOH preparation showing segmented fungal hyphae (short arrows). Note the dissolution of the nail plate (long arrow) precluding evaluation for penetrating hyphae (oil × 1,000).

  • View in gallery

    Fungal hyphae seen on surgical pathology diagnostic testing (arrows, PAS stain × 400; inset, oil × 1,000).

  • 1

    Scher RK, Tulumbus B, Argo L, et al: The nurse’s role in diagnosing onychomycosis. .Dermatol Nurs 7::335. ,1995. .

  • 2

    Elewski BE: Clinical pearl: diagnosis of onychomycosis. .J Am Acad Dermatol 32::500. ,1995. .

  • 3

    Zaias N: Onychomycosis. .Dermatol Clin 3::445. ,1985. .

  • 4

    Cohen J, Scher R, Pappert A: “The Nail and Fungus Infections,” in Cutaneous Fungal Infections, ed by B Elewski, p 106, Igaku-Shoin Medical Publishers, New York, 1992..

  • 5

    Rosen T: New approaches to the diagnosis and management of onychomycosis. International Symposium, Monaco, April 1–2, 1993. .Int J Dermatol 33::292. ,1994. .

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 6

    Conant MA: The AIDS epidemic. .J Am Acad Dermatol 31 (suppl)::S47. ,1994. .

  • 7

    Achten G, Wanet-Rouard J: Onychomycoses in the laboratory. .Mykosen Suppl 23::125. ,1978. .

  • 8

    Haneke E: Fungal infections of the nail. .Semin Dermatol 10::41. ,1991. .

  • 9

    Scher RK: Onychomycosis is more than a cosmetic problem. .Br J Dermatol 130 (suppl 43)::15. ,1994. .

  • 10

    Milles CL, Riley PA, Kessenich CR: Onychomycosis: diagnosis and systemic treatment. .Nurse Pract 23::40. ,1998. .

  • 11

    Elewski BE: Diagnostic techniques for confirming onychomycosis. .J Am Acad Dermatol 35 (suppl)::S6. ,1998. .

  • 12

    Mehregan DA, Mehregan DR, Rinker A: Onychomycosis. .Cutis 59::247. ,1997. .

  • 13

    Lawry MA, Haneke E, Strobeck K, et al: Methods for diagnosing onychomycosis: a comparative study and review of the literature. .Arch Dermatol 136::1112. ,2000. .

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 14

    Suarez SM, Silvers DN, Scher RK, et al: Histologic evaluation of nail clippings for diagnosing onychomycosis. .Arch Dermatol 127::1517. ,1991. .

  • 15

    Machler BC, Kirsner RS, Elgart GW: Routine histologic examination for the diagnosis of onychomycosis: an evaluation of sensitivity and specificity. .Cutis 61::217. ,1998. .

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 16

    Scherer WP, Kinmon K: Dermatophyte test medium culture versus mycology laboratory analysis for suspected onychomycosis: a study of 100 cases in a geriatric population. .JAPMA 90::450. ,2000. .

    • Search Google Scholar
    • Export Citation
  • 17

    Scher RK, Ackerman AB: Subtle clues to diagnosis from biopsies of nails: histologic differential diagnosis of onychomycosis and psoriasis of the nail unit from cornified cells of the nail bed alone. .Am J Dermatopathol 2::55. ,1980. .

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 18

    Lemont H: Pathologic and diagnostic considerations in onychomycosis. .JAPMA 87::498. ,1997. .

  • 19

    Tosti A, Piraccini BM, Lorenzi S: Onychomycosis caused by nondermatophytic molds: clinical features and response to treatment of 59 cases. .J Am Acad Dermatol 42::217. ,2000. .

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 20

    Gianni C, Cerri A, Crosti C: Non-dermatophytic onychomycosis: an underestimated entity? A study of 51 cases. .Mycoses 43::29. ,2000. .

Onychomycosis: An Analysis of 50 Cases and a Comparison of Diagnostic Techniques

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  • 1 Staff Pathologist, Parkway Regional Medical Center, Department of Pathology, 160 NW 170th St, North Miami Beach, FL 33169.
  • | 2 Staff Podiatrist, Parkway Regional Medical Center, Department of Surgery, North Miami Beach, FL.
  • | 3 Fellow, Ackerman Academy of Dermatopathology, New York, NY.

Onychomycosis is an extremely common condition that is increasing in prevalence. Although often innocuous, it may be complicated by discomfort and secondary bacterial infections. Recently introduced oral medications may be highly effective in the eradication of this condition; however, they may carry with them significant expense and potentially serious side effects. Prior to the initiation of antifungal oral therapy, definitive diagnosis is mandatory. This study compares the sensitivity of potassium hydroxide (KOH) preparations, surgical pathology diagnostic testing (SPDT), and culture techniques for the detection of onychomycosis in 50 cases of clinically suspected onychomycosis. Analysis showed that SPDT was significantly more sensitive when compared to KOH and culture. The results suggest that SPDT may be the true gold standard for the diagnosis of onychomycosis. (J Am Podiatr Med Assoc 91(7): 351-355, 2001)

Onychomycosis is an extremely common condition that is increasing in prevalence. Although often innocuous, it may be complicated by discomfort and secondary bacterial infections. Recently introduced oral medications may be highly effective in the eradication of this condition; however, they may carry with them significant expense and potentially serious side effects. Prior to the initiation of antifungal oral therapy, definitive diagnosis is mandatory. This study compares the sensitivity of potassium hydroxide (KOH) preparations, surgical pathology diagnostic testing (SPDT), and culture techniques for the detection of onychomycosis in 50 cases of clinically suspected onychomycosis. Analysis showed that SPDT was significantly more sensitive when compared to KOH and culture. The results suggest that SPDT may be the true gold standard for the diagnosis of onychomycosis. (J Am Podiatr Med Assoc 91(7): 351-355, 2001)

In recent years, the arrival of new, highly effective agents for the eradication of onychomycosis has dramatically changed the clinician’s approach to patient care. In particular, several new oral antifungal agents have proven to be very useful in the treatment of onychomycosis. Because such therapies may carry with them significant expense and the potential for adverse side effects, it is important for the diagnosis of onychomycosis to be accurate, prompting treatment only in instances where there is the potential for definite patient benefit.

Traditionally, culture techniques using various types of specialized media have been the most commonly used methods for the diagnosis of onychomycosis. In the office setting, potassium hydroxide (KOH) preparations also have been useful for clinicians, with rapidity as their main benefit. Histologic analysis of nail plate biopsies, or surgical pathology diagnostic testing (SPDT), is yet another method to establish the diagnosis of onychomycosis. Although these various techniques have their distinct advantages, comparisons that assess their usefulness in the clinical setting are lacking in the literature. The relative sensitivity, specificity, and cost-effectiveness of culture techniques as compared to KOH preparations and SPDT have not been tested adequately. The purpose of this study was to determine the relative usefulness of SPDT as compared with KOH preparations and standard culture techniques for the identification of onychomycosis. The sensitivity of each test in the detection of fungal elements was recorded. In addition, the ability of each test to detect specific fungal elements (ie, hyphal and yeast forms) was determined.

Materials and Methods

Fifty consecutive cases of clinically suspected pedal onychomycosis at the Parkway Regional Medical Center in North Miami Beach, Florida, were studied. All cases in which antifungal therapy (either topical or systemic) had been used within the 3 months prior to sampling were excluded. In each case, the method of collection was standard manual debridement. All specimens were transferred for processing in sterile bags, without fixative. The fresh specimen was fragmented and divided into three aliquots of equal size. The three separate aliquots were then submitted for SPDT, KOH analysis, and culture.

For histologic analysis, 4-micron sections were obtained from processed, formalin embedded tissue, and stained with both hematoxylin and eosin (H&E) and periodic acid-Schiff reaction (PAS). The various samples were evaluated microscopically for the presence of fungal elements (yeasts and hyphae). Special attention was directed toward the identification of hyphae with penetration into the nail plate matrix.

The KOH preparations were made by placing sampled tissue on a glass slide with 20% KOH. The procedure was hastened with an external heat source. The specimen was evaluated microscopically for the presence of fungal elements (yeasts and hyphae). The microscopic assessments were performed in a double-blind fashion.

Specimen cultures were performed on Dermatophyte Test Medium (DTM) and Sabouraud dextrose agar (Becton Dickinson Microbiology Systems, Cockeysville, Maryland). Cultures were maintained for 4 weeks and checked periodically for growth as indicated by changes in media color.

Results

Nail samples from 50 patients with clinically suspected onychomycosis were examined using KOH dissolution, culture, and SPDT. The patient population included 31 females and 19 males, ranging in age from 11 to 98 years, with a mean age of 56 years. Patients (16 females, 12 males) whose nail plates disclosed hyphal elements by SPDT ranged from 17 to 86 years of age, with a mean age of 54 years.

The KOH preparations disclosed fungal elements in 16 of the 50 tested cases. Examination for the presence of penetrating hyphae was precluded secondary to tissue dissolution in all cases (Fig. 1). Twelve cases were culture-positive: eight were positive on Sabouraud dextrose agar, three on DTM, and two on both. When SPDT was applied to sampled tissue, 36 cases were positive for fungal elements (hyphae and/or yeast forms). Twenty-eight of these cases showed hyphal elements, all of which could be seen within the substance of their respective nail plates (Fig. 2). Both SPDT and KOH preparations allowed for differentiation between hyphae and yeast forms in all positive cases. The study data are presented in Table 1.

Statistical Analysis

A contingency table was constructed to determine differences among the sensitivities of KOH preparations, SPDT, and cultures for the diagnosis of onychomycosis. Chi-square analysis demonstrated statistically significant differences between the three tests (P = .001). A Fisher exact two-tailed test was then used to determine the relationship between tests. Analysis showed that SPDT was significantly more sensitive when compared directly with KOH (P = .001) and culture (P = .001). There was no significant difference between sensitivity of KOH and cultures (P = .100).

Discussion

The management of onychomycosis has gained renewed interest in recent years due to the increasing prevalence of the condition and the introduction of new medications with better efficacy to treat it. In the United States, fungal infections account for approximately 50% of all nail problems1, 2 and occur in 15% to 20% of all persons between 40 and 60 years of age.3 Pedal onychomycosis is approximately four times more prevalent than onychomycosis arising in the fingernail.4 Among the factors responsible for the high number of cases in the general population are the aging of the population, an increased number of immunocompromised patients, and an increasingly active and athletic population.5-8

In and of itself, onychomycosis is not typically of clinical significance, but if left untreated, such infections may lead to secondary ulceration, paronychia, and cellulitis. Restrictive footwear or shoes with narrow toe-boxes may lead to discomfort that may become severe enough to interfere with professional and recreational activities. Diabetic patients are especially prone to onychomycosis-related complications secondary to microvascular and neurologic impairment. In addition, infected nails may have an aesthetically unpleasant appearance, leading to adverse social stigmata and a negative effect on self-esteem and social interaction.9

A definitive diagnosis of onychomycosis is crucial before prescribing oral antifungal agents because of the risk of adverse side effects, toxic drug interactions, and ballooning costs.10 The currently accepted diagnostic modalities for the identification of onychomycosis include the KOH preparation, fungal cultures, and SPDT.11 Although studies comparing these modalities have found their way into the dermatologic literature,12-15 the publication of such studies in podiatric publications has been rare.16 Despite the benefit of its relative rapidity, the present study suggests that the utility of KOH preparations may be limited because of its lack of sensitivity as compared to SPDT. This observation led Scher and Ackerman17 to suggest nail plate biopsy in clinically suspicious cases when KOH preparations are consistently negative. Moreover, owing to the dissolution of the keratogenous matrix of the nail plate, the presence of penetrating hyphae cannot be assessed. The determination of hyphae penetration into the nail plate may be helpful to distinguish pathogenic organisms from nonpathogenic surface contaminants. The ability to invade and colonize the nail plate defines pathogenicity.18

Cultures have been considered the gold standard for the diagnosis of onychomycosis; however, these techniques are not without significant limitations. Even under ideal conditions, fungi may take as long as a month to grow. While DTM cultures may be quicker, they are not reliable for detecting the presence of nondermatophytes. Investigators19, 20 have shown that nondermatophytes are responsible for a significant number of clinically suspected onychomycosis cases. Additionally, organism viability and culturability may be affected by environmental conditions during transportation. This is of considerable significance when shipping specimens to remote labs. In the present study, the combination of DTM and Sabouraud dextrose agar culture techniques demonstrated organisms in only 43% of cases in which hyphae were demonstrated by SPDT. When observing the specific culture techniques independently, they proved comparatively less sensitive. Neither culture techniques nor KOH preparations provided a lasting, easily accessible record for documentation of the test result, an advantage of the histologic sections used in SPDT. This finding may be of particular importance in high-volume podiatric practices that are at increased risk for third-party investigations.

Clinical appearance alone is not sufficient to make the determination of onychomycosis. Of the 50 suspected cases of onychomycosis reviewed in this study, hyphae were demonstrated histologically in only 28 cases, and in only 12 cases could the organisms be confirmed by culture. Some of these negative cultures represent instances in which nail abnormalities are caused by diseases that clinically mimic onychomycosis (eg, psoriasis, lichen planus, trauma, nail tumors, spongiotic dermatitides, and ischemic conditions). Many negative cultures, however, represent actual false-negative results as demonstrated by the concurrently performed SPDT. Clinicians should be aware that a negative culture does not entirely rule out a fungal infection.

In summary, onychomycosis is a mycotic infection, pathologically defined by the invasion of hyphae into the nails of the fingers or toes. Onychomycosis is not clinically distinctive and may be mimicked by numerous other infectious and noninfectious conditions that make its confirmation mandatory prior to medical treatment. Recent therapeutic advances have included effective oral medications for this condition, although many such therapies are associated with significant cost and may have serious side effects. This study has shown SPDT to be statistically more sensitive than culture techniques or KOH preparations in detecting hyphal elements in cases of clinically suspected onychomycosis. The results suggest that SPDT may be a more appropriate gold standard for the diagnosis of onychomycosis and also demonstrate the need for larger studies to test this hypothesis.

Figure 1. KOH preparation showing segmented fungal hyphae (short arrows). Note the dissolution of the nail plate (long arrow) precluding evaluation for penetrating hyphae (oil × 1,000).
Figure 1.

KOH preparation showing segmented fungal hyphae (short arrows). Note the dissolution of the nail plate (long arrow) precluding evaluation for penetrating hyphae (oil × 1,000).

Citation: Journal of the American Podiatric Medical Association 91, 7; 10.7547/87507315-91-7-351

Figure 2. Fungal hyphae seen on surgical pathology diagnostic testing (arrows, PAS stain × 400; inset, oil × 1,000).
Figure 2.

Fungal hyphae seen on surgical pathology diagnostic testing (arrows, PAS stain × 400; inset, oil × 1,000).

Citation: Journal of the American Podiatric Medical Association 91, 7; 10.7547/87507315-91-7-351

Table 1.

Study Results

Table 1.

Eugene McCoy and William Velez for preparation of high-quality microscopic slides; Martha Castro, Bruno Jean, Farnoosh Ebrahimi, and Raquel Solorzano for outstanding microbiology work.

  • 1

    Scher RK, Tulumbus B, Argo L, et al: The nurse’s role in diagnosing onychomycosis. .Dermatol Nurs 7::335. ,1995. .

  • 2

    Elewski BE: Clinical pearl: diagnosis of onychomycosis. .J Am Acad Dermatol 32::500. ,1995. .

  • 3

    Zaias N: Onychomycosis. .Dermatol Clin 3::445. ,1985. .

  • 4

    Cohen J, Scher R, Pappert A: “The Nail and Fungus Infections,” in Cutaneous Fungal Infections, ed by B Elewski, p 106, Igaku-Shoin Medical Publishers, New York, 1992..

  • 5

    Rosen T: New approaches to the diagnosis and management of onychomycosis. International Symposium, Monaco, April 1–2, 1993. .Int J Dermatol 33::292. ,1994. .

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 6

    Conant MA: The AIDS epidemic. .J Am Acad Dermatol 31 (suppl)::S47. ,1994. .

  • 7

    Achten G, Wanet-Rouard J: Onychomycoses in the laboratory. .Mykosen Suppl 23::125. ,1978. .

  • 8

    Haneke E: Fungal infections of the nail. .Semin Dermatol 10::41. ,1991. .

  • 9

    Scher RK: Onychomycosis is more than a cosmetic problem. .Br J Dermatol 130 (suppl 43)::15. ,1994. .

  • 10

    Milles CL, Riley PA, Kessenich CR: Onychomycosis: diagnosis and systemic treatment. .Nurse Pract 23::40. ,1998. .

  • 11

    Elewski BE: Diagnostic techniques for confirming onychomycosis. .J Am Acad Dermatol 35 (suppl)::S6. ,1998. .

  • 12

    Mehregan DA, Mehregan DR, Rinker A: Onychomycosis. .Cutis 59::247. ,1997. .

  • 13

    Lawry MA, Haneke E, Strobeck K, et al: Methods for diagnosing onychomycosis: a comparative study and review of the literature. .Arch Dermatol 136::1112. ,2000. .

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 14

    Suarez SM, Silvers DN, Scher RK, et al: Histologic evaluation of nail clippings for diagnosing onychomycosis. .Arch Dermatol 127::1517. ,1991. .

  • 15

    Machler BC, Kirsner RS, Elgart GW: Routine histologic examination for the diagnosis of onychomycosis: an evaluation of sensitivity and specificity. .Cutis 61::217. ,1998. .

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 16

    Scherer WP, Kinmon K: Dermatophyte test medium culture versus mycology laboratory analysis for suspected onychomycosis: a study of 100 cases in a geriatric population. .JAPMA 90::450. ,2000. .

    • Search Google Scholar
    • Export Citation
  • 17

    Scher RK, Ackerman AB: Subtle clues to diagnosis from biopsies of nails: histologic differential diagnosis of onychomycosis and psoriasis of the nail unit from cornified cells of the nail bed alone. .Am J Dermatopathol 2::55. ,1980. .

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 18

    Lemont H: Pathologic and diagnostic considerations in onychomycosis. .JAPMA 87::498. ,1997. .

  • 19

    Tosti A, Piraccini BM, Lorenzi S: Onychomycosis caused by nondermatophytic molds: clinical features and response to treatment of 59 cases. .J Am Acad Dermatol 42::217. ,2000. .

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 20

    Gianni C, Cerri A, Crosti C: Non-dermatophytic onychomycosis: an underestimated entity? A study of 51 cases. .Mycoses 43::29. ,2000. .