Differential Diagnosis for Pitted Nail

Single most likely diagnosis

• Traumatic nail plate injury: The patient's history of biting a piece of skin off around the nail 2 months prior is a strong indicator that the pitted nail is a result of this traumatic injury, which can cause damage to the nail matrix leading to nail plate abnormalities.

Other Likely diagnoses

• Onychomycosis: A fungal infection of the nail can cause pitting, but it typically presents with other symptoms such as thickening, discoloration, or brittleness of the nail.
• Psoriasis: Nail psoriasis can cause pitting, and given the timeframe, it's possible that the patient has an underlying psoriatic condition that was triggered or exacerbated by the trauma.
• Eczema (Dyshidrotic): Eczema around the nail can lead to nail changes including pitting, especially if the condition is severe or chronic.

Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)

• Squamous cell carcinoma: Although rare, a history of trauma followed by nail changes could potentially be a sign of a malignant process, especially if there are other signs such as persistent ulceration or unexplained pain.
• Melanoma: Nail melanoma (subungual melanoma) can present with nail plate changes, including pitting, and is critical to diagnose early due to its high mortality rate if left untreated.

Rare diagnoses

• Alopecia areata: This autoimmune condition can cause nail pitting, among other symptoms like hair loss, but it's less common than other causes of nail pitting.
• Lichen planus: Nail involvement in lichen planus can lead to pitting, but it's part of a broader spectrum of symptoms that typically include skin and mucous membrane lesions.
• Sarcoidosis: A systemic disease that can affect multiple parts of the body, including the nails, causing pitting among other nail abnormalities, but it's a rare condition.