Dermatological diagnosis in dogs. An approach based on cli by Grupo Asís

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Maite Verde Arribas

DERMATOLOGICAL DIAGNOSIS IN DOGS

An approach based on clinical patterns

DERMATOLOGICAL DIAGNOSIS IN DOGS An approach based on clinical patterns Maite Verde Arribas

DERMATOLOGICAL DIAGNOSIS IN DOGS

An approach based on clinical patterns

Maite Verde Arribas

Dermatological diagnosis in dogs

DERMATOLOGICAL DIAGNOSIS IN DOGS An approach based on clinical patterns Maite Verde Arribas

AUTHOR: Maite Verde Arribas. FORMAT: 22 × 28 cm. NUMBER OF PAGES: 160. NUMBER OF IMAGES: 330. BINDING: hardcover.

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Using a variety of graphical resources, this atlas describes the cutaneous clinical patterns most commonly encountered in dogs (accounting for 90 % of cases seen in veterinary clinics), as well as the associated aetiologies. For each pattern, corresponding guidelines are provided to ensure correct diagnosis. This book has been designed as an educational guide for veterinary practitioners to facilitate the diagnosis of skin diseases. The wealth of graphical material complementing the text provides veterinary surgeons with reference images with which to compare the cases they encounter in the clinic.

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Dermatological diagnosis in dogs. An approach based on clinical patterns

Presentation of the book Most veterinary surgeons who treat pets are generalists, and deal every day with cases of all kinds that can involve any organ system. Skin conditions are extremely common, accounting for between 15 % and 25 % of daily consultations. General practitioners working in the field of clinical dermatology thus need tools that allow them to approach and guide the diagnostic process in a straightforward way from the moment they see the patient. Therefore, when designing the structure of this book, The author selected a format that would allow the reader to learn about dermatology as they apply the principals and protocols explained within. The author believes that the simplest and most logical way to approach a dermatological clinical case is to observe the patientâ&#x20AC;&#x2122;s appearance and the predominant lesions and their distribution, and to link this information to a clinical pattern. By creating a list of possible causes of the clinical pattern in question, veterinary surgeons can identify the most probable causes based on information in the patientâ&#x20AC;&#x2122;s clinical history. If they have also identified the appropriate diagnostic tests, and the order in which they should be performed, it is highly likely that a definitive diagnosis of most cutaneous processes can be established by a veterinary surgeon without in-depth knowledge of dermatology. The first 2 chapters provide a general introduction to diagnosis based on clinical patterns, and describe the general characteristics of the skinâ&#x20AC;&#x2122;s response to aggressions in general, its response to aggressions that produce lesions, and the characteristics of the resulting clinical patterns. The subsequent 5 chapters are dedicated to the most commonly encountered patterns: multifocal alopecia; generalised alopecia; scaling/crusting and seborrhoeic; erosive-ulcerative; and papulopustular and vesicular. The last chapter deals specifically with the diagnosis of pruritus. The content is designed to allow readers to learn by following a systematic approach to resolving canine dermatological problems. The format is that of a small canine dermatological atlas, with over 300 images accompanying the text. This book will provide students and veterinary surgeons with a deeper knowledge of dermatology.

Dermatological diagnosis in dogs. An approach based on clinical patterns

The author Maite Verde Arribas Maite Verde graduated in Veterinary Medicine from the Faculty of Veterinary Medicine of the University of Zaragoza. She holds a PhD in Veterinary Medicine and is a Professor of Animal Medicine and Surgery. She has served as vice-dean of Clinical Services and dean of the Faculty of Zaragoza (1995–2003), as well as vice-president and president of AVEPA (Spanish Association of Small Animal Specialists, 2006–2012). She has been a member of the council of the European Association of Establishments for Veterinary Education (EAEVE) (2002–2004), is a current member of the National Commission on Veterinary Specialties of the Spanish Council of Veterinary Colleges, and is the director of the Veterinary Hospital of the University of Zaragoza.

She has published several works and book chapters on dermatology and internal veterinary medicine and has spoken at congresses and seminars for both academia and private industry.

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A Professor of Internal Medicine and Dermatology, AVEPA-accredited in Dermatology and Internal Medicine, she is a member of the European Society of Dermatology (ESVD) and has participated in the organisation of the 3 European ESVD congresses held in Spain. She has also served as secretary and president of GEDA, AVEPA’s group of experts in dermatology. She currently heads the Dermatology Service of the Veterinary Hospital of the University of Zaragoza.

Communication services Website Online visualisation of the sample chapter. Presentation brochure in PDF format. AuthorÂ´s CV. Sample chapter compatible with iPad.

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DERMATOLOGICAL DIAGNOSIS IN DOGS An approach based on clinical patterns Maite Verde Arribas

Table of contents 1. General considerations for diagnosis based on clinical patterns Introduction Identify and define the dermatological pattern Collect basic information Establish the list of possible causes of the pattern Propose tests in a logical order

2. Defining cutaneous patterns Introduction Pathophysiological responses of the epidermis to aggressions of the skin Hyperkeratosis: alterations in the cornification process Acanthosis: epidermal hyperplasia Apoptosis Necrosis Atrophy of the epidermis Alterations in the epidermal fluid equilibrium Acantholysis Exocytosis

Cutaneous clinical patterns Focal-multifocal alopecia pattern Symmetrical alopecia pattern (regional or generalised) Scaling/crusting and seborrhoeic pattern Erosive-ulcerative pattern Vesicular papulopustular pattern Nodular pattern Pigmentary alteration pattern Pruritus

3. Focal or multifocal alopecia Introduction Underlying causes of the pattern Diagnostic procedure Analysis of the medical history General examination Dermatological examination Diagnostic protocol

4. Symmetrical alopecia (regional or generalised) Introduction Factors involved in hair growth and formation

Underlying causes of the pattern

Pathophysiological responses of the dermis to skin aggressions

Diagnostic procedure

Pathophysiological responses of skin appendages

General examination

Pathophysiological responses of the adipose tissue

Diagnostic protocol

Analysis of the medical history Dermatological examination

5. Scaling/crusting and seborrhoeic pattern Introduction Underlying causes of the pattern

8. When the clinical presentation is pruritus Introduction Pathophysiology of pruritus

Primary keratinisation alterations

Causes of pruritic signs

Secondary keratinisation alterations

Diagnostic procedure

Analysis of the medical history

Characteristics of pruritus

General examination

Dermatological examination

Diagnostic protocol

6. Erosive-ulcerative pattern Introduction Underlying causes of the pattern Diagnostic procedure Analysis of the medical history General examination Dermatological examination Diagnostic protocol

7. Papulopustular andÂ vesicular pattern Introduction Underlying causes of the pattern Diagnostic procedure Analysis of the medical history General examination Dermatological examination Diagnostic protocol

Treatment

9. References

DERMATOLOGICAL DIAGNOSIS IN DOGS An approach based on clinical patterns

INTRODUCTION Analysis of clinical patterns is the simplest way diagnose dermatological problems, since this approach is based on the natural observation of cutaneous alterations that a patient presents in the clinic (Figs.Â 1â&#x20AC;&#x201C;3). When basing the diagnosis on dermatological patterns, it is not necessary to be familiar with all skin diseases, which are very numerous. It is sufficient to characterise the type of lesions (BoxÂ 1) displayed by the patient and then follow the logical steps of a diagnostic protocol. Establishing a dermatological diagnosis this way is possible thanks to significant advances in our understanding of the causes of cutaneous pathologies in dogs, and the corresponding presentations. In the early 1970s, when the field of veterinary dermatology was in its infancy, the information available was scarce, or uncorroborated. Since then, advances in this field have made it possible to establish simpler diagnostic frameworks based on proven scientific knowledge. Now, after 40 years of progress in canine dermatology, establishing a diagnosis based on clinical patterns is the most practical way to learn dermatology and to teach it to veterinary students and clinicians in general.

02 Papulopustular and generalised alopecia pattern.

01 Multifocal alopecia pattern. Expertise in dermatology is not required to apply a diagnostic protocol based on clinical patterns. Obviously, this process will be easier for veterinary surgeons with more experience, since they will be familiar with the information and will have applied this systematic approach more frequently in the past. However, each veterinary surgeon can use this diagnostic approach, adapting it to their own circumstances.

The key to using this system is knowing where to look, and thus acquiring the habit of properly identifying skin lesions and their distribution.

03 Erosive-ulcerative pattern.

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GENERAL CONSIDERATIONS FOR DIAGNOSIS BASED ON CLINICAL PATTERNS

BOX 1 Main lesions and their corresponding dermatological patterns SCALING/CRUSTING AND SEBORRHOEIC PATTERN

Scales

Crusts

Comedones

Follicular casts

EROSIVE-ULCERATIVE PATTERN

Erosions

Ulcers

It is also necessary to know how to identify crucial information in the medical history in order to create a list of differential diagnoses and perform the appropriate diagnostic tests for the clinical presentation in question. To establish a diagnosis based on clinical patterns, one must know how to identify primary skin lesions, and to associate them with a predominant morphological pattern. Here lies the key to success: if we fail to correctly identify the morphological pattern, we begin based on an erroneous premise, making it more difficult to reach a correct diagnosis.

PAPULOPUSTULAR AND VESICULAR PATTERN

Papules

Pustules

Vesicles

Collarettes

NODULAR PATTERN

Nodules

The following are the central pillars of diagnosis based on clinical patterns: » Identify and define the dermatological pattern after performing a dermatological examination and observing the lesions. » Collect basic information on the characteristics of the patient from the medical history and based on the general and dermatological examination (Boxes 2 and 3). » Create a list of possible causes of the observed pattern. » In a logical order, list the tests necessary to identify the underlying cause of the clinical picture.

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DERMATOLOGICAL DIAGNOSIS IN DOGS An approach based on clinical patterns

IDENTIFY AND DEFINE THE DERMATOLOGICAL PATTERN In most cases, it will be easy to recognise the main types of cutaneous lesions found in dogs, and to characterise the dermatological pattern. However, in some cases it is difficult to identify a predominant pattern, as the lesions observed may correspond to several different patterns. In this situation it is necessary to identify the predominant pattern. For example, if there are numerous areas or foci of alopecia across the body, in addition to 3 or 4 papulopustular lesions (Fig. 4), the main pattern would be characterised as multifocal alopecia and the papulonodular lesions would be considered secondary. Conversely, if the patient has 3 or 4 foci of nodular alopecia in a body region (Fig. 5), the pattern would be considered nodular, and the alopecia in nodular areas would be considered secondary, or of lesser importance.

04 Papulopustular lesions in a case of multifocal alopecia.

To determine the predominant clinical pattern, it is also necessary to look at the types of lesions and their location. In each case it is useful to note the following aspects and to illustrate the information collected in the examination on a silhouette (Fig. 6): » Whether the distribution is symmetric or asymmetric. » The affected area or region: head, neck (dorsal and ventral), trunk (dorsal and ventral), limbs, and tail. » Affected areas subjected to pressure, rubbing, or friction. » Affected mucocutaneous areas (lips, nostrils, eyelids, foreskin, and vulva), areas of the muzzle, pinnae, or footpads. » Affected mucosa: oral, conjunctival, anal, and genital.

Types of lesions: colour changes, papules, pustules, vesicles, scaling, crusts, follicular casts, collarettes, alopecia, nodules, erosions, and ulcers. The characteristics of the lesions in terms of shape, regular/ irregular appearance, and pigmentation.

Figure 7a shows a case of multifocal alopecia of the left hindlimb, and Figure 7b shows the corresponding lesions marked on a silhouette. From the information obtained, we can establish the dermatological pattern: » Easily removable or absent hair: » Focal/multifocal alopecia pattern – distributed in foci or round patches. » Symmetrical generalised alopecia pattern – homogeneously distributed and affecting large areas. » Prevalence of scales and/or crusts on the skin surface: scaling/crusting and seborrhoeic or exfoliative dermatosis pattern – multifocal, regional, or generalised distribution. » Lack of continuity or integrity in the epithelium with predominance of erosive-ulcerative lesions: erosive-ulcerative pattern. » Lesions that are raised relative to the skin surface: » Papulopustular and vesicular pattern, with predominance of papular, pustular, vesicular, or bullous lesions, with fluid content. » Nodular pattern, with predominantly solid, raised lesions, consisting mainly of nodules, plaques, or warts. » Changes in the colour of the skin or hair with no other lesions: pigmentary alteration pattern.

05 Papulonodular alopecia.

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GENERAL CONSIDERATIONS FORÂ DIAGNOSIS BASED ON CLINICAL PATTERNS

on which lesion location and distribution is indicated. Silhouettes of the right and left side, as well as dorsal and ventral views, 06 Silhouettes should be used.

Focal erythematous alopecia on the hindlimb produced by Microsporum canis. (b) Silhouette indicating the corresponding lesions 07 (a) observed in the patient in 7a.

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DERMATOLOGICAL DIAGNOSIS IN DOGS An approach based on clinical patterns

COLLECT BASIC INFORMATION Data on the dog’s age, breed, and sex, as well as information extracted from the medical history (Box 2) and obtained in the general and dermatological examinations (Box 3) will help in reaching a diagnosis. A detailed clinical history is the simplest and most important element required to establish a diagnosis in dermatology. The duration of the problem, the age of onset, the evolution of the disease, the seasonality of the condition, information on littermates or other siblings, the nature and distribution of the clinical signs, and the dog’s response to medical treatment should all be discussed with the owner. It is also important to consider the presence of other pets, the patient’s diet, whether the patient lives indoors or outdoors, bed type, deworming and vaccination programs, and any previous treatments and their effects. Any observations or concerns mentioned by the owner should also be noted in chronological order.

ESTABLISH THE LIST OF POSSIBLE CAUSES OF THE PATTERN Regardless of whether the clinician can identify a cause for a given pattern, this book provides the relevant information on the different causes of cutaneous pathologies and lists the aetiologies associated with each clinical pattern.

PROPOSE TESTS IN A LOGICAL ORDER Once the list of differential diagnoses has been drawn up, it is necessary to consider the tests required to confirm or rule out possible causes in order to ultimately identify the cause of the clinical pattern. To this end, we begin by establishing the order of precedence of the causes based on the information obtained from the medical history and the examination. Each of the chapters of this book describes the diagnostic procedures recommended for each dermatological pattern, as well as the order in which tests should be conducted to reach a definitive diagnosis.

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GENERAL CONSIDERATIONS FOR DIAGNOSIS BASED ON CLINICAL PATTERNS

BOX 2 Clinical history for dermatological processes Name of pet

Are clinical signs worse indoors or outdoors?

Age

■ ■ ■

Sex

Breed

How long has the dog had this skin condition? ___________ __________________________________________________ Are there periods during which lesion intensity or itching is reduced?

■ ■

Yes (specify when) _________________ No

■

It began ________________

The first affected area was ________________

■ ■

Yes (specify to which areas) ________________ No

Muzzle Ears Eyes Neck

■ ■ ■ ■

Chest Back Abdomen Tail

■ ■ ■ ■ ■ ■

Dogs

■

Cats

■

Rodents

■

Farm animals

■

Don’t know

Has been at home Has visited somewhere else

Record all medicines the patient has received to treat the skin problem, and their effects. Drug

Dose

Duration

Effect

Axillae Groin Hindlimbs Forepaws Hindlimbs Hindpaws

Indicate how many:

■

Yes

Has your dog been at home for the last few months, or has it visited a nursery, hairdresser, fair, or the home of friends or family?

Does the patient share its environment with other animals? Birds

■

Rabbits

Do these animals have skin problems?

Does the dog have any of the following signs? (Check if yes).

■ ■ ■

■ ■

Cough Sneezing

Vomiting Diarrhoea

Watery eyes

■ ■ ■

■

Does the dog have a normal appetite?

Yes (specify what type) ________________ No

Percentage of time the dog spends indoors (____ %) and outdoors (____ %).

Drinks excessively Urinates excessively Flaccidity

Has the dog had ear infection problems?

Yes (specify what type) ________________

People who live with the dog. Do they have skin problems?

■ ■

Do the clinical signs show seasonality?

Mark the parts of the body that your dog scratches, licks, sucks, or rubs:

■ ■

No change

Have any of the dog’s relatives had skin problems?

Has it spread?

■ ■ ■ ■

Worse outdoors

Yes (specify) ________________

How did it start and what area was affected?

■ ■

Worse indoors

■

Yes

■ ■

Has the dog’s character changed?

■

Yes

■

Additional comments ________________

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DERMATOLOGICAL DIAGNOSIS IN DOGS An approach based on clinical patterns

UNDERLYING CAUSES OF THE PATTERN

DIAGNOSTIC PROCEDURE Having introduced the concept of the clinical pattern of focal or multifocal alopecia, we will next consider the procedure to follow to determine the cause, discussing the factors to be considered at each stage, and the interpretation thereof.

Before examining a dog with focal or multifocal alopecia, it is helpful to prepare a list of possible causes of this clinical pattern (Box 1 and Fig. 6).

BOX 1 Main causes of focal or multifocal alopecia patterns »

Sebaceous adenitis1

Postvaccinal alopecia

Leishmaniasis2

Alopecia areata

Demodicosis2

Epitheliotropic lymphoma

Cicatricial alopecia

Dermatophytosis

Cutaneous lupus

Cyclic alopecia

Familial dermatomyositis

Discoid lupus

Pattern alopecia

Ischaemic dermatopathy

Follicular arrest1

Traction alopecia

Zinc-responsive dermatosis

Pemphigus foliaceus

Follicular dysplasia/dystrophy

Pemphigus vulgaris

Bacterial folliculitis2

Vasculitis

Tail gland hyperplasia

1 2

Drug-induced alopecia (corticosteroids, progestogens) Postclipping alopecia

Multifocal alopecia that can become generalised. Very frequent presentation.

Zinc deficiency

Bacterial folliculitis Dermatophytosis Demodicosis

Epitheliotropic lymphoma Sebaceous adenitis

Pemphigus

showing a 06 Schematic hair follicle, in which the Alopecia areata

Ischaemic dermatopathy

areas affected by some of the main causes of canine focal and multifocal alopecia are indicated.

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FOCAL OR MULTIFOCAL ALOPECIA

To establish a definitive diagnosis of the process underlying focal or multifocal alopecia, it is necessary to analyse the patient’s clinical history, perform general and dermatological examinations, and finally, to propose a sequence of diagnostic tests to rule out potential causes.

1-year old). However, they can also occur in geriatric (Fig. 9a) or young adult dogs (Fig. 9b) that have any type of metabolic or infectious alteration, neoplasm, or endocrinopathy, or have received immunosuppressive treatment for long periods. In most young dogs, dermatomyositis (Fig. 10) is characterised by vascular lesions and hair loss. Most cases of atopy occur in patients aged between 6 months and 3 years, and present with bacterial folliculitis (Fig. 11). Epitheliotropic lymphoma, which can be associated with alopecia (Fig. 12), is observed in older dogs (generally over 7 years of age).

ANALYSIS Of THE MEDICAL HISTORY The following are the most important factors to be considered when diagnosing dogs with focal or multifocal alopecia. » Age. Diseases such as demodicosis (Fig. 7) and dermatophytosis (Fig. 8) are very common in young dogs (less than

08 Eight-month-old dog with dermatophyte lesions.

07 Six-month-old dog with demodicosis. a

09 Demodicosis in (a) a geriatric dog with hyperadrenocorticism and (b) a patient with leishmaniasis. 37

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DERMATOLOGICAL DIAGNOSIS IN DOGS An approach based on clinical patterns

Reversible and irreversible alopecia The appearance of hair in the alopecic area will depend on the type of inflammatory reaction, vasculopathy, or aggression in question, as well as the extent of the lesions and the chronicity of the process. » Demodicosis. Most cases of alopecia due to demodicosis resolve fully. Mites penetrate deep into the hair follicle, causing folliculitis. As the process worsens, the follicular structures rupture, giving rise to furunculosis, with very deep lesions that affect a large amount of hair. If these lesions progress to eschars, there will be no possibility of hair regrowth in the affected areas. » Dermatophytosis. Fungal hyphae fracture the hair shaft, but once the infected hair enters telogen phase and is lost, the new hair that replaces it is usually healthy. » Sebaceous adenitis. Destruction of the sebaceous glands induces follicular hyperkeratosis and partial or total alopecia of the affected area. In sebaceous adenitis, permanent alopecia can be prevented by quickly controlling the process. » Alopecia areata. Activated lymphocytes attack the components of the follicle and the hair bulb, resulting in loss of the hair shaft. This process is reversible in most cases. » Irreversible alopecia. Irreversible forms of alopecia include congenital alopecia, follicular dysplasia, colour dilution alopecia, and, in general, any alopecia of genetic origin. For example, hereditary dermatomyositis of Collies follows a course of follicular atrophy and perifollicular fibrosis in many cases, with complete loss of the hair follicles (irreversible alopecia). Irreversible alopecia can also be caused by deep bacterial pyoderma that presents with furunculosis; burns; radiotherapy; or ischaemia that gives rise to necrotising folliculitis with permanent destruction of the follicles and cicatricial alopecia. Neoplasms that affect the dermis can directly destroy hair follicles. Epitheliotropic cutaneous lymphoma (mycosis fungoides) can cause alopecia due to the invasion of the follicular epithelium by neoplastic lymphocytes.

DIAGNOSTIC PROTOCOL To establish a definitive diagnosis of focal or multifocal alopecia, several laboratory tests should be performed, in the following order:

STEP

Brushing and combing

Brushing of the patient’s hair can reveal the presence of large parasites, such as fleas or Trombicula larvae, which can cause mechanical pruritus or allergic itching accompanied by secondary bacterial folliculitis. A fine-toothed comb should be used, paying particular attention to the ventral area of the neck and trunk, as well as the dorsolumbar zone.

STEP

Deep and superficial skin scraping

This approach can be used to confirm or rule out the involvement of microorganisms, particularly those of the genus Demodex (Fig. 27), and any other mites that live on the epidermal surface. Scraping is performed with a spatula or a scalpel blade that has been coated in mineral oil to promote adhesion of the material. For superficial scrapings, samples can be obtained by simply rubbing in the direction of hair growth over the alopecic area. For deep scrapings, a fold of skin is held between the index finger and thumb, and the skin squeezed while scraping in the direction of hair growth until capillary bleeding is observed.

Considerations when performing a skin scraping »

In cases of dogs with long hair, first clip the hair in the area to be scraped.

Avoid scraping in ulcerated areas.

Scrapings should be performed in areas containing primary lesions, such as papules or pustules.

A drop of mineral oil is placed on the spatula or scalpel blade and the material obtained is immediately transferred to a slide and then observed under an optical microscope at low magnification (4× or 10×).

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FOCAL OR MULTIFOCAL ALOPECIA

scraping samples in which (a) Demodex canis and (b) Trombicula autumnalis mites are visible. 27 Skin Image (b) courtesy of Amparo Ortúñez.

STEP

Trichogram

This allows identification of the current phase of the hair growth cycle by determining whether anagen or telogen roots predominate. Using this technique, it is also possible to observe shafts showing structural alterations or signs of invasion by fungal spores in the medulla and cortex (Fig. 28). Lactophenol blue can be used to better visualise spores; affected hair shafts are stained blue while healthy shafts remain unstained.

Medulla and cortex of a hair shaft (upper part) 28 Trichogram. that has lost its structure due to invasion by fungal spores. In the lower part of the shaft the hair structure is normal.

The accumulation of disorganised melanin in the roots and shafts is indicative of follicular dystrophies associated with different colour haircoats (Fig. 29). Hairs that resemble an exclamation mark are observed in cases of alopecia areata. Follicular casts (Figs. 30 and 31) are characteristic of a variety of follicular processes, including demodicosis, dermatophytosis, sebaceous adenitis, and some endocrine processes.

Accumulations of melanin in the hair of a dog 29 Trichogram. with hair-colour-associated follicular dystrophy.

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DERMATOLOGICAL DIAGNOSIS IN DOGS An approach based on clinical patterns

Follicular cast on the hair of a dog with follicular 30 Trichogram. dystrophy.

31Trichogram. Follicular casts in a dog with sebaceous adenitis.

Tricography allows analysis of the status of the hair, revealing anomalies in both the roots and the hair shaft, and enables distinction of true from false alopecia based on examination of the tips.

STEP

Wood’s lamp

Greenish fluorescence allows visualisation of infestations caused by Microsporum canis (Fig. 32), but not superficial mycoses produced by other dermatophyte fungi.

Wood’s lamp Considerations when interpreting results

lamp produces fluorescence of the haircoat of a 32 AdogWood’s infested with M. canis.

Preparation of the lamp.The lamp should be turned on at least 2 minutes before use to allow it to stabilise.

The examination should be conducted in a dark room, holding the lamp 5 to 10 cm from the skin surface.

Positive fluorescence is that which is visible on the shaft of the affected hair.

False positives: topical products such as Vaseline, which emits violet fluorescence; salicylic acid, which emits greenish fluorescence; white clothing (robes, work overalls), which can produce bluish-white fluorescence; scales, dandruff, or certain bacteria, such as Pseudomonas aeruginosa and Corynebacterium; and certain soaps.

False negatives: previous treatments with topical fungicides such as povidone and captan.

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