# When Hashimoto’s Thyroiditis Masks Biermer’s Disease: A Revealing Case of Autoimmune Polyendocrinopathy

## TL;DR

A patient with Hashimoto’s thyroiditis was found to also have Biermer’s disease, highlighting the importance of screening for related autoimmune conditions.

## Contribution

This case highlights the effectiveness of oral vitamin B12 supplementation in autoimmune-related deficiency and emphasizes the link between Hashimoto’s and Biermer’s disease.

## Key findings

- A patient with autoimmune hypothyroidism was found to have Biermer’s disease without neurological or digestive symptoms.
- Oral vitamin B12 supplementation effectively corrected the deficiency, challenging the standard intramuscular treatment approach.
- The case underscores the need for systematic screening for vitamin B12 deficiency in autoimmune thyroiditis patients.

## Abstract

Biermer's disease is an autoimmune disorder characterized by atrophic gastritis leading to vitamin B12 deficiency, often revealed late due to non-specific symptoms. It may be associated with other autoimmune pathologies, notably Hashimoto's thyroiditis, as part of a type 3b autoimmune polyendocrinopathy (AIP). We report the case of a 44-year-old female patient, followed for autoimmune hypothyroidism, in whom vitamin B12 deficiency was detected. The patient showed no suggestive signs such as glossitis, paresthesia, or other neurological abnormalities. Investigations confirmed Biermer's disease, with no neurological or digestive involvement. Treatment with oral vitamin B12 rapidly corrected the deficiency. While intramuscular vitamin B12 is commonly preferred in autoimmune-related deficiencies, oral supplementation was chosen in this case and proved effective, despite not being the standard approach. This case illustrates the value of systematic vitamin B12 screening in patients with autoimmune thyroiditis and, conversely, the need to monitor thyroid function in any patient with Biermer's disease.