Enfoque evolutivo

• Subcutaneous zygomycosis or subcutaneous phycomycosis (SP) has two clinically and mycologically distinctive entities termed as basidiobolomycosis (etiological agent:

Basidiobolus ranarum) and conidio-bolomycosis (etiological agent: Conidiobolus Fig. 8.30: Rhinosporidiosis–pink friable polypoidal

growth over the root of the nose

Fig. 8.31: Rhinosporidiosis–noduloplaque lesions over the arms

coronatus). These organisms belonging to Entomophthorales cause granulomatous infection that usually affects healthy people.

• SP due to Conidiobolus is uncommon.

Clinically, the disease is characterized by nasal obstruction due to the inflammation of the submucosa of the nostril, usually in the vicinity of the inferior turbinate.

• SP is also caused by Basidiobolus. The site of infection is usually confined to the limb girdles or proximal limbs. It occurs chiefly in children. Characteristically, it manifests as painless, well-circumscribed, firm to hard subcutaneous masses, which grow slowly at the periphery and may envelop parts of or a whole limb (Fig. 8.32). The border is smooth, rounded, clearly defined, and can be raised up by inserting fingers underneath it. This is thought to be an almost diagnostic clinical feature of the disease. There is no involvement of the regional lymph nodes.

Fig. 8.32: Subcutaneous phycomycosis–shiny disk like indurated lesion over the thigh, can be insinuated at the margin with fingers

Fungal Infections

71

• Differential diagnosis:

1. Lymphatic edema (no distinctive edge) 2. Subcutaneous malignant lymphoma

(grows more rapidly) 3. Subcutaneous morphea

• A therapeutic trial with potassium iodide in a clinical setting may be considered as an important criterion for diagnosis where facilities to culture the organism do not exist.

SPOROTRICHOSIS

• It is caused by Sporothrix schenckii and is characterized by nodulo-ulcerative and crusted lesions arranged in a linear fashion over the extremities with intervening lymphatics thickened like a cord.

• The best sources of diagnostic material are smears, exudates, and biopsies (to look for

“Asteroid bodies”). S. schenckii is very rarely seen in direct microscopic examination because yeasts are usually present only in small numbers; the organism can be readily isolated on Sabouraud’s agar.

• Differential diagnosis:

1. Fish tank granuloma 2. Cutaneous leishmaniasis

• Potassium iodide (saturated solution) is effective in the cutaneous types of sporotrichosis.

Other deep fungal infections: Cryptococcosis and aspergillosis are ubiquitous throughout the world. In south east Asia, penicillinosis is common whereas coccidioidomycosis and histoplasmosis are restricted to certain geographic regions.

CRYPTOCOCCOSIS

• Cryptococcosis is an opportunistic infection caused by the encapsulated yeast Cryptococcus neoformans.

• Virtually all infections involve the central nervous system, with meningitis the most frequent manifestation.

• Cutaneous dissemination occurs in 10% to 20% of patients, has a variable presentation and may precede other signs of infection.

• Initial signs of cryptococcosis include cellulitis, genital or oral ulcerations, or molluscum-, herpes simplex-, or Kaposi’s sarcoma- like lesions.

• Diagnosis can be made by performing curettage on a lesion, by making a potassium hydroxide preparation, India ink preparation, isolation of fungus on culture or by a biopsy of lesion. Cryptococcal antigen is present in these patient sera and can be detected by latex particle agglutination.

• Intravenous amphotericin B alone or with flucytosine and oral fluconazole is highly effective in the treatment of cryptococcus infection.

PENICILLIOSIS

• Penicillium marneffei is the only penicillium species that is dimorphic and can cause systemic mycosis in human beings, particularly those who are immuno-compromised.

• Features of the infection frequently include fever, anemia, marked weight loss, cough and diarrhea, but skin eruptions occur in the majority.

• Cutaneous manifestations usually consist of a generalised papular eruption, in which the papules may be umbilicated (due to central necrosis), although necrotic papules, nodules, folliculitis, macular rash and mouth ulcer have also been reported.

• Diagnosis depends on isolation of the organism from blood or tissue.

• Treatment includes systemic amphotericin B, itraconazole or fluconazole.

9 Infestations

SCABIES (THE ITCH, SEVEN YEAR ITCH)

• Causative agent: Sarcoptes scabiei var. hominis (Fig. 9.1)

• Morphology: The mite has an ovoid body, flattened dorsoventrally. The body is creamy white marked with transverse corrugations, and on its dorsal surface by bristles and spines (denticles). The mite has four pairs of short legs. The rear two pairs of legs of female mites end in long bristles called setae. Adult female mite measures about 0.4 × 0.3 mm whereas adult male about 0.2 × 0.15 mm. The mite prefers non-hairy skin and areas of low sebum production.

• Life cycle: Copulation occurs in burrows excavated by female mite in stratum corneum. After copulation, the pregnant female enlarges the burrows and begins egg laying. It travels 5 mm per day and lays 40-50 eggs during its life span of 4-6 weeks (Figs 9.2 and 9.3). These eggs hatch in a week and reach maturity (eggs-larvae-nymph-adult) in about 3 weeks.

• Most infected adults harbor 10 to 12 mites

• Mode of spread-close personal contact, but may be transmitted through clothing, or towels.

• Incubation period- when a human is infested for the first time, symptoms usually

Fig. 9.1: Sarcoptes scabiei mite (300-400 microns) Fig. 9.2: Eggs and fecal pellets of sarcoptes

Infestations

73

develop after 3-6 weeks while after reinfestation, they occur within 1 or 2 days.

• The classic symptom is intense pruritus especially at night in bed

• The sites of predilection are the interdigital spaces (Fig. 9.4), wrists, points of elbows, antecubital fossae, the anterior axillary folds, the umbilicus (Fig. 9.5), and the genitalia (Fig.

9.6) especially the gluteal cleft (Fig. 9.7) (“circle of Hebra”).

• The most diagnostic or pathognomonic finding is an intact “S” shaped or linear burrow with a papule or vesicle at its end housing the mite (Fig. 9.8). Most common Fig. 9.4: Scabies – typical finger web spaces involvement with papular, vesicular and crusted lesions

Fig. 9.5: Scabies – periumbilical papular lesions

Fig. 9.6: Scabies – genital and thigh area involved by papular and excoriated lesions

Fig. 9.7: Scabies – papular lesions over the gluteal area

Fig. 9.3: An egg of sarcoptes

sites are webspaces of the hands, wrists, and lateral aspect of palms.

• Generalized urticarial papules, excoriations and eczematous changes are secondary lesions caused by sensitization to the mite.

• Tiny scaly papules on the nipple and male genitalia (glans, shaft and scrotum) are pathognomonic of scabies.

• Infants and small children often have vesicular lesions on the palms, soles, head and neck (Figs. 9.9 and 9.10). Scabies in babies is generally more extensive in distribution of burrows, vesicular or vesicopustular lesions on the hands and feet, extensive eczematization, multiple crusted nodules on the trunk and limbs.

• Nodular scabies- in some cases, itching nodules (5–20 mm in diameter, red, pink, tan or brown in color) persist for several months.

They are found most commonly on the scrotum (Fig. 9.11). Burrow may be seen on the surface of early nodules.

• Scabies incognito means modified clinical picture of classical scabies which mimic other dermatoses due to inappropriate use of topical steroids.

• Complications of scabies: Secondary infection of skin lesions, eczematization, nephritogenic strains of streptococci may produce secondary sepsis, and glomeru-lonephritis particularly in tropics.

Fig. 9.8: Scabies—typical burrows of scabies of the shaft of the penis

Fig. 9.9: Scabies in an infant—papulovesicular lesions in finger web spaces

Fig. 9.10: Scabies in an infant – vesicular, pustular and crusted lesions on the ankle and feet

Infestations

75

• Diagnosis: If a mite is demonstrated, one needs no diagnostic criteria. Typical lesions on the penis and nipple, the presence of burrows even without a mite and interdigital lesions are almost diagnostic. Severe pruritus, especially at night, of short duration or in family members is also very suggestive.

• Burrow identification (Ink method): The suspected burrow is smeared with blue or black fountain pen ink and then wiped off with an alcohol swab after some time. The dye that enters the burrows is highlighted as a dark line.

• Microscopic examination: The burrow is scraped with 15 no. blade and examine the material with 10% KOH or mineral oil under light micrscope. Presence of mite, egg or fecal concretions (scybala) confirms diagnosis of scabies.

• Under dermoscope, mite in burrow resembles “jet with contrail”.

• Differential diagnosis:

A. For pruritic localized or generalized rash: In infants: Papular urticaria, infantile acropustulosis, In children:

Papular urticaria, insect bite reactions,

atopic dermatitis, animal scabies, In adults: acute generalized lichen planus, adverse drug reactions, contact dermatitis, pediculosis pubis, pediculosis corporis, different forms of prurigo, In elderly: Dermatitis herpetiformis, senile pruritis, delusional parasitosis.

B. For pruritic nodules: Urticaria pigmentosa, papular urticaria (insect bite), and pseudolymphoma.

• Therapy: Permethrin (5%) cream is treatment of choice (single overnight application below neck all over the body with a second application after an interval of a week). It is the treatment of choice for infants (application includes head and neck also).

Sulfur and crotamiton are safe in pregnancy.

Other agents used are gamma benzene hexachloride lotion (1%), benzyl benzoate lotion (12.5% for infants and children, 25%

for adults), esdepallethrine 0.63%, malathion 0.5% lotion, ivermectin 0.8% lotion, and monosulfiram (25%) diluted with two or three parts of water to form an emulsion.

Ivermectin 200 microgram per kg body weight single oral dose is also effective in many cases of ordinary scabies, but presumably because of lack of ovicidal activity, higher cure rates are obtained with two doses separated by an interval of a week.

It is a useful modality of treatment for institutional outbreaks of scabies as it is cheap, effective and easy to administer.

• Pruritus may persist for up to 1-2 weeks after the end of effective treatment.

• Treat infested individuals as well as close physical contacts simultaneously.

• Bedding and clothing should be washed in hot cycle of washing machine.

• Intralesional triamcinolone 5-10 mg / ml in each lesion is used for nodular scabies besides routine scabies treatment.

Fig. 9.11: Nodular scabies—nodules seen over the scrotum

CRUSTED SCABIES