An Unexpected Etiology of Rhizomelic Pseudo-Polyarthritis (Polymyalgia Rheumatica) in the Elderly

Introduction: Rhizomelic pseudo-polyarthritis or polymyalgia rheumatica (PMR) is a common chronic inflammatory rheumatism in the elderly. Its etiologies are by far dominated by giant cell arteritis and cancers. Other exceptional etiologies can be seen, and present a real diagnostic challenge for clinicians.
We report an unusual case of PMR caused by primary hypothyroidism.

Case Report: A 68-year-old patient, with no notable pathological history, was hospitalized for exploration of a PMR non-responding to corticosteroids prescribed by the family doctor. The somatic examination was without abnormalities. Extensive investigations have eliminated possible associated giant cell arteritis, connective tissue diseases, necrotizing vasculitis, infections, osteomalacia, cancer, andhaematological malignancies. Thyroid assessment revealed primary hypothyroidism with fT4 at 4.24 Pmol/l and TSH at 54.16 μmol/ml. Under thyroxine, the evolution was favorable with disappearance of any rhizomelic symptomatology.

Conclusion: This observation reports an exceptional and often overlooked etiology of PMR, which is easy to find and treat. Its knowledge by clinicians makes it possible, in certain cases, to avoid several invasive explorations as well as an unjustified corticosteroid treatment that is not devoid of side effects, sometimes severe in frail elderly subjects.

Keywords: Rhizomelic pseudo-polyarthritis, polymyalgia rheumatica, hypothyroidism, elderly.