Familial inflammatory inclusion body myositis

Abstract

Objective: To compare familial inflammatory inclusion body myositis (IBM) with hereditary inclusion body myopathies and sporadic IBM.

Patients and methods: Clinical, biological, MRI, and histological data were analysed in two siblings with inflammatory IBM and compared with those of patients with sporadic and hereditary IBM.

Results: Both patients had a clinical phenotype of sporadic IBM, which differs from hereditary myopathies because of late age of onset--respectively 65 and 66 years, and different pattern of muscular involvement--asymmetric, mainly distal but also involving quadriceps. MRI showed selective fatty infiltration and oedema in the extensor compartment of thigh muscles. The diagnosis of IBM was confirmed by muscle biopsy, showing muscle fibres containing numerous rimmed vacuoles, a characteristic shared by all types of IBM. In contrast with hereditary IBM, histological analysis also showed inflammatory mononuclear infiltrate invading non-necrotic fibres, ragged red and oxidase c negative fibres, and positive Congo red staining. Moreover, HLA class II typing disclosed DR beta 1 0301 haplotype, which is significantly related to sporadic but not to hereditary IBM. With steroid treatment and monthly intravenous immunoglobulins, the disease was stabilised in both patients at protracted follow up.

Conclusion: Sporadic and familial inflammatory IBM share the same clinical, biological, MRI, and histological features.

Figure 1

Pedigree of the family.

Figure 2

Axial spin echo T₁ and STIR images through the mid-portion of the two thighs (patient 1). Spin echo T₁ image (upper) shows fatty infiltration (high signal intensity areas) predominant in both quadricipital groups and in the posterior group of the right thigh. STIR image (lower) demonstrates oedema mostly in the quadricipital group (arrow).

Figure 3

Cryostat anterior tibial muscle biopsy specimen showing (A) non-necrotic fibres surrounded by mononuclear inflammatory cells at the endomysium and perimysium; (B) typical red-rimmed vacuoles. Light microscopy. Haematoxylin and eosin x250 and x400.