Endonyx Onychomycosis

Present features

Absent features

Normal nail plate surface

Superficial desquamation

Normal nail plate thickness

Hyperkeratosis

Nail plate firmly attached to the nail bed

Onycholysis

Milky-white nail plate discoloration

Subungual changes

Nail plate fungal hyphae

Periungual inflammation

Diagnostic Clues

Endonyx onychomycosis should be distinguished from proximal subungual onychomycosis as both present with white nail discoloration without onycholysis or subungual hyperkeratosis. History and clinical examination can help in differential diagnosis. In EO invasion occurs from distal margin, and nail discoloration starts distally and progresses proximally (Fig. 6.1) in contrast with proximal subungual onychomycosis (PSO) that originates proximally and progresses distally.

Fig. 6.1

Endonyx onychomycosis of the fingernail. The nail plate shows distal leukonychia in the absence of subungual hyperkeratosis (Courtesy of Chinmanat Tangjaturonrusamee MD )

Diagnosis of endonyx onychomycosis should be confirmed by direct microscopic examination and fungal cultures. Periodic acid-Schiff (PAS) stain will demonstrate tunnels of fungal elements arranged either longitudinally or transversely within the entire thickness of the nail plate [4, 6]. Importantly, there are no signs of fungal invasion or inflammation in the nail bed [4]. Culture of the nail clippings will expose the causative organism [6].

Summary for the Clinician

Endonyx is a rare form of onychomycosis that affects all ages and both genders. Clinicians should be aware of the presentation of this rare entity, as certain forms may be resistant to standard antifungal therapy [6]. The presence of milky-white discoloration of the nail plate in the absence of hyperkeratosis and onycholysis suggests endonyx pattern [4]. PAS staining for fungal elements confined to the nail plate may help validate the diagnosis [4]. Consider treatment with standard topical and oral antifungals first, followed by combination therapy, chemical and/or surgical plate avulsion, or photodynamic therapy if the infection is difficult to treat.

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