Pemphigus Revealing Profound Hypothyroidism: A Rare Association

Pemphigus vulgaris is a rare autoimmune bullous dermatosis, and while Hashimoto's thyroiditis is the leading cause of hypothyroidism, their association falls within the spectrum of polyautoimmunity. A 50-year-old female patient with no specific past medical history presented with a four-month history of a clinical picture combining erosive mucocutaneous bullous lesions and significant asthenia. Further history-taking revealed that the patient exhibited significant psychomotor retardation, accompanied by subtle systemic signs (psychomotor slowness, bradycardia, and lower limb edema). A thyroid workup was performed accordingly, revealing severe hypothyroidism (ultra-sensitive thyroid-stimulating hormone > 68 IU/L, with severely depressed free T4 secondary to Hashimoto's thyroiditis, which was confirmed by the positivity of anti-thyroid peroxidase antibodies and thyroid ultrasonography. The management initially combined general corticosteroid therapy with prednisone and hormone replacement therapy with levothyroxine, resulting in a favorable clinical outcome after two months of treatment for the pemphigus and the normalization of thyroid hormone levels. This association, although rare, is reported in the literature. It is explained by the existence of a common genetic background, notably involving certain HLA system haplotypes, as well as a global immune dysregulation favoring the emergence of multiple autoimmune pathologies in the same individual. This clinical observation highlights the importance of systematic screening for other autoimmune diseases, particularly thyroid disorders, in all patients with pemphigus.