Black piedra should be differentiated from other diseases presenting as red, pruritic, annular, scaly rash. The differentials include the following:
|Name of superficial infection||Clinical presentation||Extension to hair follicle||Fungus(i)||Systemic disease||KOH preparations||Morphology in tissue sections|
|Tinea or ringworm||Round lesions with scaly border, accompanied by pruritis and burning||Yes; when suppurative known as kerion, when chronic known as Majocchi's granuloma||Dermatophytes (Epidermophyton spp., Trichophyton spp., Microsporum spp.)||Very rare but can invade the dermis and soft tissues, causing mycetomas||Hyphae with or without septations||Hyphae cannot be visualized in the keratin with H&E, special stains are needed|
|Tinea versicolor||Hypo and hyperpigmentation in patients with oily and sweaty skin, fine scales when scratching||Yes, known as Pityrosporum folliculits||Malassezia spp.||Systemic infections may occur in premature neonates receiving parenteral nutrition and in other immunosuppressed hosts||Yeasts and hyphae (“spaghetti and meat balls”)||Faintly basophilic hyphae in the stratum corneum|
|Tinea nigra||Brown to black macule, usually on palms, with some scaling||No||Phaeoannellomyces werneckii||Not described||Darkly pigmented, septated, and branching hyphae||Pigmented hyphae in the stratum corneum|
|White piedra||Creamy-white, small, soft nodules in hair shafts||No||Trichosporon spp.||Immunosuppressed patients may have lung infiltrates, renal involvement, and fungemia||Septate hyphae perpendicular to hair shaft||Not used for diagnosis|
|Black piedra||Hard dark nodules in hair shafts||No||Piedraia hortae||Not described||Collections of crescent ascospores surrounded by pigmented hyphae||Not used for diagnosis|
|Superficial candidiasis||Intertrigo, chronic paronychia, onychodystrophy, cheilitis||Yes||Candida spp.||Yes, particularly in patients with AIDS and depending on the level of immunosuppression||Yeasts, pseudohyphae may be observed||Fungal elements may be seen through the biopsy, vascular invasion must be determined|
Under a relatively-low magnification of 100X, this photomicrograph reveals some of the pathologic morphology displayed by a primate hair shaft indicative of the disease known as, “black piedra”, also known as “trichosporosis”, which is caused by the fungal organism, Piedraia hortae. From Public Health Image Library (PHIL). 
- "eMedicine - Piedra : Article by Robert A Schwartz". Retrieved 2008-11-08.
- Gip L (1994). "Black piedra: the first case treated with terbinafine (Lamisil)". The British journal of dermatology. 130 Suppl 43: 26–8. PMID 8186138. Unknown parameter
- "Public Health Image Library (PHIL)".