Investigations
Investigations to consider
bacterial skin swab
Test
A skin swab may be sent for polymerase chain reaction/Gram stain following recurrent or persistent episodes of folliculitis to confirm the aetiology of the folliculitis.
Performed when there is a definite pustule that can be unroofed with a No.15 blade.
Result
gram-positive cocci typical of Staphylococcus aureus infection
viral skin swab
Test
Polymerase chain reaction (PCR) for herpes simplex virus or varicella (or Tzanck smear if PCR not available) hould be performed when clinical history and physical examination (e.g., vesicles and ulcerations) are suggestive of Herpes simplex infection.
In experienced hands, Tzanck smear has been reported to have 80% sensitivity and 90% specificity.[34]
Result
moulding and clustering of keratinocytes to form multinucleated giant cells are suggestive of Herpes simplex infection
skin scraping for mycology
Test
Indicated when clinical history suggests fungal aetiology or condition does not respond to therapy for bacterial folliculitis.
Result
presence of hyphal forms suggestive of dermatophyte infection
tissue culture
Test
Bacterial culture identifies the causative organism and is helpful in selecting targeted antibacterial therapy.
Fungal culture is sometimes helpful in directing antifungal therapy.
Viral culture is sometimes obtained for suspected viral folliculitis, in addition to DFA assay and skin biopsy.
Result
bacterial, fungal, and viral cultures identify causative organism
skin biopsy
Test
Bacterial and fungal folliculitis: neutrophils infiltrating the walls and lumen of the hair follicles, with variable admix of lymphocytes and macrophages depending on the chronicity of folliculitis.
Often, micro-organisms can be seen within the hair follicle.
Viral folliculitis: lymphocyte infiltrate in the walls and lumen of the hair follicles.
Demodex folliculitis: the mite Demodex folliculorum is seen within the hair follicle. Perifollicular lymphohistiocytic inflammation is often seen.
Result
bacterial and fungal folliculitis reveal predominantly neutrophilic infiltrate in the walls and lumen of the hair follicle; viral folliculitis reveals predominantly lymphocytic infiltrate in the walls and lumen of the hair follicle
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