How can I differentiate between onychomycosis and other nail disorders in a primary care setting?

In a primary care setting, differentiating onychomycosis from other nail disorders involves a careful clinical assessment combined with appropriate diagnostic testing. Clinically, onychomycosis typically presents as nail discoloration (yellow, white, or brown), thickening, and onycholysis (separation of the nail from the nail bed), often accompanied by subungual debris and nail brittleness. These features are more suggestive of fungal infection compared to other nail disorders such as psoriasis, lichen planus, trauma, or nail dystrophies, which may have overlapping but distinct patterns like pitting, ridging, or uniform nail thickening without debris ¹.

Primary care assessment should include a detailed history focusing on symptom duration, exposure risks (e.g., communal bathing, occlusive footwear), and any associated skin fungal infections such as tinea pedis, which commonly coexist and support a diagnosis of onychomycosis ¹. Physical examination should note the pattern of nail involvement—distal subungual, superficial white, or proximal subungual—which can guide suspicion towards fungal etiology ².

To confirm diagnosis and differentiate from other nail disorders, nail sampling for fungal microscopy and culture is recommended, especially if initial topical treatment fails or diagnosis is uncertain. This helps exclude non-fungal causes and identify the causative organism, which is crucial for targeted therapy ¹,². In some cases, referral to podiatry or dermatology may be necessary for improved specimen collection or biopsy if diagnosis remains unclear ².

Other nail disorders such as psoriasis or lichen planus often have characteristic clinical signs (e.g., nail pitting, oil spots, or longitudinal ridging) and may require different management; thus, distinguishing features on examination and history are key (Mayeaux, 2000; Biesbroeck and Fleckman, 2015). Additionally, trauma-related nail changes usually have a clear history of injury and lack fungal elements on microscopy ¹.

In summary, differentiation relies on clinical features, history, and confirmatory fungal investigations. Persistent or atypical cases warrant specialist referral for further evaluation ¹,².