Sporotrichosis

Description:

Sporotrichosis is primarily a chronic mycotic infection of the cutaneous or subcutaneous tissues and adjacent lymphatics characterized by nodular lesions which may suppurate and ulcerate. Infections are caused by the traumatic implantation of the fungus into the skin, or very rarely, by inhalation into the lungs. Secondary spread to articular surfaces, bone and muscle is not infrequent, and the infection may also occasionally involve the central nervous system, lungs or genitourinary tract.

Clinical manifestations:

Fixed cutaneous sporotrichosis: Primary lesions develop at the site of implantation of the fungus, usually at more exposed sites mainly the limbs, hands and fingers. Lesions often start out as a painless nodule which soon become palpable and ulcerate often discharging a serous or purulent fluid. Importantly, lesions remain localised around the initial site of implantation and do not spread along the lymphangitic channels. Isolates from these lesions usually grow well at 35C, but not at 37C.

Fixed cutaneous sporotrichosis showing an ulcerating lesion on the leg.

Lymphocutaneous sporotrichosis: Primary lesions develop at the site of implantation of the fungus, but secondary lesions also appear along the lymphangitic channels which follow the same indolent course as the primary lesion ie they start out as painless nodules which soon become palpable and ulcerate. No systemic symptoms are present. Isolates from these lesions usually grow well at both 35C and 37C.

Lymphocutaneous sporotrichosis showing typical elevated subcutaneous nodules developing along the regional lymphatics of the forearm.

Lymphocutaneous sporotrichosis showing more advanced, ulcerating lesions developing along the lymph system of the forearm.

Pulmonary sporotrichosis: This is a rare entity usually caused by the inhalation of conidia but cases of haematogenous dissemination have been reported. Symptoms are nonspecific and include cough, sputum production, fever, weight loss and upper-lobe lesion. Haemoptysis may occur and it can be massive and fatal. The natural course of the lung lesion is gradual progression to death.

Osteoarticular sporotrichosis: Most patients also have cutaneous lesions and present with stiffness and pain in a large joint, usually the knee, elbow, ankle or wrist. Osteomyelitis seldom occurs without arthritis; the lesions usually confined to the long bones near affected joints.

Other rare forms of sporotrichoisis include endophthalmitis, chorioretinitis and meningitis.

Laboratory diagnosis:

1. Clinical material: A tissue biopsy is the best specimen.

2. Direct Microscopy: Tissue sections should be stained using PAS digest, Grocott's methenamine silver (GMS) or Gram stain.

Section from a fixed cutaneous lesion showing round Periodic Acid-Schiff (PAS) positive budding yeast-like cells. Sporothrix schenckii is a dimorphic fungus and this is the typical yeast-like form seen in tissue.

Interpretation: Look for small narrow base budding yeast cells (2-5um). Note they are often present in very low numbers and may be difficult to find. PAS and GMS stains are essential.

3. Culture: Clinical specimens should be inoculated onto primary isolation media, like Sabouraud's dextrose agar and Brain heart infusion agar supplemented with 5% sheep blood.

Interpretation: A positive culture from a biopsy should be considered significant.

4. Serology: Serological tests are of limited value in the diagnosis of Sporotrichosis.

5. Identification: Hyphomycete characterized by thermal dimorphism and clusters of ovoid, denticulate conidia produced sympodially on short conidiophores.

Causative agents:

Sporothrix schenckii

Management:

Cutaneous lesions respond well to saturated potassium iodide [4-6 ml three time a day for 2-4 months], however itraconazole [400 mg/day] and terbinafine [250 mg twice daily] have both proved to be effective, although treatment times may be long. Ideally, treatment needs to be maintained for at least a month after clinical cure is achieved. Local heat has also been shown to improve cutaneous lesions. Extracutaneous forms of sporotrichosis may need a combination of antifungal treatment with Amphotericin B or itraconazole together with surgical debridement.

Further reading:

Ajello L and R.J. Hay. 1997. Medical Mycology Vol 4 Topley & Wilson's Microbiology and Infectious Infections. 9th Edition, Arnold London.

Elewski BE. 1992. Cutaneous fungal infections. Topics in dermatology. Igaku-Shoin, New York and Tokyo.

Kwon-Chung KJ and JE Bennett 1992. Medical Mycology Lea & Febiger.

Richardson MD and DW Warnock. 1993. Fungal Infection: Diagnosis and Management. Blackwell Scientific Publications, London.

Rippon JW. 1988. Medical Mycology WB Saunders Co.