Differential Diagnosis for 16-year-old Male with Alopecia

Single Most Likely Diagnosis

• Alopecia Areata: Given the patient's age and family history of alopecia, alopecia areata is a strong consideration. It is an autoimmune condition that can lead to patchy hair loss and has a genetic predisposition. The patient's thyroid function tests (TSH and T4) are abnormal, which can be associated with autoimmune thyroiditis, a condition sometimes linked with alopecia areata.

Other Likely Diagnoses

• Thyroid Disorder (Hyperthyroidism): The patient's low TSH (0.39) and slightly low T4 (1.3) levels may indicate hyperthyroidism, especially if the T4 is not adjusted for the assay used. Hyperthyroidism can cause hair loss, among other symptoms. However, the T4 level provided is on the lower end, which might not typically align with hyperthyroidism unless it's a case of T4-to-T3 conversion issue or assay variability.
• Androgenetic Alopecia: Although less common in a 16-year-old, androgenetic alopecia (male pattern baldness) could be considered, especially with a family history. However, the age of onset and the pattern of hair loss would be atypical for this condition.

Do Not Miss Diagnoses

• Pituitary or Hypothalamic Disorder: Abnormal thyroid function tests could be indicative of a pituitary or hypothalamic issue affecting thyroid-stimulating hormone (TSH) secretion. These conditions can have significant health implications and might also lead to hair loss among a myriad of other symptoms.
• Autoimmune Polyendocrine Syndrome (APS): Given the potential for autoimmune thyroid disease (suggested by abnormal TSH and T4 levels) and alopecia areata, APS should be considered. This condition involves multiple endocrine gland failures and can be associated with autoimmune diseases like alopecia areata.

Rare Diagnoses

• Syphilis: Although rare, syphilis can cause hair loss (alopecia) and has been associated with a variety of skin and systemic manifestations. It's less likely but should be considered in the differential diagnosis, especially if other risk factors are present.
• Systemic Lupus Erythematosus (SLE): SLE is an autoimmune disease that can cause hair loss, among many other symptoms. It's less common in males and would typically present with a constellation of other findings, but it remains a rare consideration in this case.