Proliferative myositis

Proliferative myositis (PM) refers tois a rare benign inflammatory myopathy. It is sometimes classified as a subtype of a pseudosarcomatous proliferative soft-tissue lesion.

Epidemiology

It is thoughtThought to commonly occur in middle aged-aged adults (i.e. around(around 50 years), but has also been described in children.

Clinical presentation

Patients may present with a rapidly enlarging solitary, firm and painful  soft soft-tissue mass involving the affected region.

Pathology

It is characterized by infiltration of basophilic giant cells and proliferative fibroblasts within the affected region. Its exact aetiology is not well known although an antecedent recent local trauma has been documented in some cases.

Location

There may a predilection for the head and neck region or upper extremities ⁴.

Radiographic features

Ultrasound

Described features include patchy areas of hyperechogenicity, containing hypoechoic lines preservation of continuous muscle bundles.

MRI

• T2: may show an ill-defined, hyperintense, intramuscular lesion, containing isointense lines ²
• C (Gd): there may be subtotal enhancement with non-enhancing geometrical web and fascial enhancement sometimes been described ²

Treatment and prognosis

Its clinical course is benign and local recurrence following simple excision is considered uncommon.

History and etymology

It was first described by H E Kern in 1960.

See also

• WHO 2002 soft tissue tumour classification system