Differential Diagnosis for Thickened Nail Plate with Marked Horizontal Ridges

• Single Most Likely Diagnosis
  • Onychomycosis: This is a fungal infection of the nail that can cause thickening and ridging of the nail plate. The horizontal ridges could be indicative of a systemic or localized infection affecting nail growth.
• Other Likely Diagnoses
  • Psoriasis: Nail psoriasis can lead to thickening of the nail plate and the formation of horizontal ridges due to inflammation and abnormal nail growth patterns.
  • Eczema/Dermatitis: Chronic eczema or dermatitis around the nail can cause changes in nail growth, leading to thickening and ridging.
  • Trauma: Repeated trauma to the nail can cause thickening and ridging as the nail grows out.
• Do Not Miss Diagnoses
  • Systemic Lupus Erythematosus (SLE): Although less common, SLE can cause nail changes, including thickening and ridging, as part of its broader spectrum of symptoms.
  • Thyroid Disorders: Both hypothyroidism and hyperthyroidism can lead to nail changes, including thickening and ridging, due to metabolic effects on nail growth.
• Rare Diagnoses
  • Darier's Disease: A rare genetic disorder that affects the skin and sometimes the nails, leading to abnormalities in nail growth and structure.
  • Yellow Nail Syndrome: Characterized by thickened, yellowish nails with horizontal ridges, often associated with lymphatic abnormalities and sometimes respiratory issues.