image of silk fabric and dry skin

A. Y. Sergeev, MD, PhD, DMSca,b, A. K. Gupta, MD, PhD, FRCPCc, Y. V. Sergeev, MD, PhD, DMSca,d

aNational Academy of Mycology, Moscow, Russia
bMoscow Medical Academy, Moscow, Russia
cDivision of Dermatology, Department of Medicine, Sunnybrook and Women’s College Health Science Center (Sunnybrook site) and the University of Toronto, Toronto, Canada
dPresidential Medical Center, Department of Dermatology, Moscow, Russia


Onychomycosis is a common disease, and there are a number of factors that may affect the duration and dosage of treatment including the type of onychomycosis, the area and thickness of nail involvement, the age of the patient, and the location of the digit that is affected. We report a composite index, the Scoring Clinical Index for Onychomycosis (SCIO) that combines these factors to give an index of the overall severity of onychomycosis. The use of the SCIO may have treatment implications; by matching patients with similar SCIO scores, it may be possible to better compare the clinical response to therapy.

Key Words:
onychomycosis, hyperkeratosis

Onychomycosis is a common superficial fungal infection, affecting between 6.5 and 12.8% of the population in North America.1 Individuals over 60 years of age are most commonly affected, with prevalence rates as high as 20-30% in this population.1 Toenails are involved to a greater extent than fingernails, and the great toenail is the most commonly affected. The clinical presentation of the onychomycosis, i.e., distal and lateral onychomycosis, superficial white onychomycosis, proximal subungual onychomycosis, and total dystrophic onychomycosis must be taken into account when therapeutic decisions are being made. The Scoring Clinical Index for Onychomycosis (SCIO index) attempts to present the severity of onychomycosis as a composite score.3-6

The SCIO Index

The clinical pattern component of the SCIO is further divided into (1) clinical form, (2) depth of nail involvement and, (3) thickness of subungual hyperkeratosis. The clinical form is taken from Zaias,2 who proposed the classification of onychomycosis into distal-lateral subungual onychomycosis (DLSO), proximal subungual onychomycosis (PSO) and superficial white onychomycosis (SWO). The depth of involvement of the onychomycosis, the degree of hyperkeratosis and the type of clinical presentation are used to calculate SCIO.

Key FactorGrade 1Grade 2Grade 3
Clinical form (f)DLSOSWOPSO
Depth of involvement (d)<1/31/3 to 2/3>2/3
Degree of hyperkeratosis (h)absent or < 1mm1 – 2 mm> 2 mm

These values are then substituted into the equation:
Clinical Index Component = [(d/3)3-f (f + h(3 – f))]1- [(2 – f)(3 – f)/2]

Using this formula, in SWO, PSO and DLSO the values will be 1, 3, and between 1 and 5, respectively.

The SCIO has a growth component in addition to the clinical index component, and this is based on the location of the onychomycosis (fingernail or toenail, digit number) and the age of the patient.

Key FactorGrade 1Grade 2Grade 3
Location (l)II – V fingernailsThumbnail or II – V toenailsBig toenail
Age of patient, years (a)<2525-60>60

The growth component may reflect the amount of therapy required for onychomycosis. The growth component value reflects approximately the time needed for complete outgrowth of the target nail. The SCIO index (range 1 to 30) is calculated using the clinical index component and the growth component in the following equation:

SCIO = [(d/3)3-f (f + h (3-f)) ( l) (a + 3)/3]1-[(2-f)(3-f)/2]

A higher SCIO index suggests that the onychomycosis may be more severe and thereby require more prolonged treatment. The proposed guidelines for treatment of onychomycosis according to SCIO values are summarized below:

SCIOTreatment approach
1-3Topical treatment: remove (cut or scrape off) affected marginal parts of the nail Use topical antifungals until healthy nail re-grows
3-6Topical treatment with lower success, which often depends on growth rate Systemic therapy recommended in slower-growing nails or proximal onychomycosis type
6-9Systemic therapy. Use scheme proposed for fingernails (e.g., itraconazole: 2 pulses of 200mg bid)
9-12Systemic therapy. Use scheme proposed for toenails (e.g., itraconazole: 3 pulses of 200mg bid)
12-16Systemic therapy. Use scheme proposed for fingernails with any antifungal (e.g., 4-5 pulses of itraconazole, 200mg bid)
16-20Combination therapy (systemic antifungal + topical measures) Adequate keratolytic treatment recommended
20-30Consider nail avulsion (e.g., with urea paste), continue with systemic therapy

To facilitate SCIO evaluation by clinicians, several utilities have been designed. Among them, is the SCIO ruler – a paper device used to obtain the SCIO values without having to make any calculations. The ruler also provides guidelines for selecting treatment strategy in onychomycosis. The same task may be performed with a SCIO electronic calculator or on a special website available at


The SCIO may enable comparison of the severity of onychomycosis between nails despite differences in the clinical presentation and demographics. The SCIO index may prove to be an accurate indicator of therapeutic effectiveness. However, further clinical studies will be required before definitive claims can be made.


  1. Gupta AK, Jain HC, Lynde CW, Macdonald P, Cooper EA, Summerbell RC. Prevalence and epidemiology of onychomycosis in patients visiting physicians’ offices: a multicenter Canadian survey of 15,000 patients. J Am Acad Dermatol 43(2 Pt 1):244-8 (2000 Aug).
  2. Zaias N. Onychomycosis. Arch Dermatol 105(2):263-74 (1972 Feb).
  3. Sergeev A. Clinical index to assess the severity of onychomycosis and the duration of systemic antifungal therapy. JEADV 1999; 12 (Suppl. 2): S. 237 (Abstract)
  4. Sergeev A. Fungal disease of the nails. Moscow 2001; 144P (Monograph) [Gribkovye zabiolevanya nogtei] (Russian)
  5. Sergeev A. Index for clinical assessment of onychomycosis and evaluation of systemic antifungal therapy duration. Moscow 1999; 32P (Monograph). [Index dlya klinicheskoi otsenki onichomycoza i rascheta prodolzhitelnosti terapii sistemnymi antimikotikami] (Russian)
  6. Sergeev A. Index for clinical assessment of onychomycosis and evaluation of systemic antifungal therapy duration. Vestn Dermatol Venerol; 2001; 2:33–40. [Index dlya klinicheskoi otsenki onichomycoza i rascheta prodolzhitelnosti terapii sistemnymi antimikotikami] (Russian).