Differential Diagnosis for Excessive Hair Loss in an 18-Month-Old Child

Single Most Likely Diagnosis

• Alopecia Areata: This is an autoimmune condition that can cause patchy hair loss. It's relatively common in children and can present at any age, including infancy. The onset can be sudden, and it may be triggered by stress or other autoimmune conditions.

Other Likely Diagnoses

• Tinea Capitis (Ringworm of the Scalp): A fungal infection that causes hair loss, often accompanied by redness, itching, and scaling of the scalp. It's contagious and common in children.
• Nutritional Deficiencies: Deficiencies in nutrients like iron, zinc, or biotin can lead to hair loss. Given the age, a diet lacking essential nutrients or difficulties with absorption could be a factor.
• Eczema or Atopic Dermatitis: While primarily a skin condition, severe cases can lead to hair loss due to constant scratching and inflammation of the scalp.
• Trichotillomania: Although less common in this age group, it's a psychological condition where the child pulls out their own hair, leading to noticeable hair loss.

Do Not Miss Diagnoses

• Congenital Hypothyroidism: Untreated hypothyroidism can lead to hair loss among other symptoms. Early detection is crucial for treatment and preventing long-term effects.
• Congenital Syphilis: A condition that can cause hair loss, among other severe health issues, if left untreated.
• Autoimmune Disorders: Conditions like lupus or rheumatoid arthritis are rare in infants but can cause hair loss and are critical to diagnose early.

Rare Diagnoses

• Congenital Alopecia: A rare condition where a child is born with little to no hair, which can be a part of various genetic syndromes.
• Netherton Syndrome: A rare genetic disorder characterized by hair loss, skin inflammation, and other systemic issues.
• Citronelle Syndrome: An extremely rare condition that affects the hair, skin, and other bodily systems, leading to hair loss and other severe symptoms.

Each of these diagnoses requires careful consideration of the child's medical history, physical examination, and potentially, further diagnostic testing to determine the underlying cause of the hair loss.