Co-existence of amyotrophic lateral sclerosis and polymyositis: a case report

Background: The diagnosis of amyotrophic lateral sclerosis (ALS) requires the careful exclusion of mimic syndromes in presence of involvement of both upper and lower motor neurons progressing over time. In the differential diagnosis myopathic processes must be considered. In particular, inclusion body myositis patients are often misdiagnosed as having ALS, due to the fact that these two conditions share some clinical and serological similarities. Other myopathies, such as polymyositis are even rarer and, as a general rule, a diagnosis of inflammatory myopathy tends to exclude ALS. Aim: Describe the case of an ALS patient that was subsequently co-diagnosed with polymyositis. Case Report: A 51-year-old woman with a 4-month history of distal muscle weakness and progressive hypotrophy at the upper limbs came to our attention. Her past medical history was significant for hypothyroidism. Neurological examination showed intact cranial nerves, diffuse mild bilateral weakness with wasting of the interossei muscles at the hands and evident fasciculations; deep tendon reflexes were increased at the upper limbs and decreased at the lower ones. Both brain and spinal cord MRI were normal, as it was the exam of the CSF. An EMG study revealed signs of acute denervation and fasciculations in both distal and proximal muscle of the arms; myopathic changes were not reported. Due to the unexpected bilateral worsening of proximal weakness at the lower limbs, the patient underwent a muscle biopsy (vastus lateralis), which revealed the coexistence of neurogenic alterations and myopathic features, compatible with an inflammatory myopathy. An oral steroid course was started but the patient failed to respond, deteriorating further until tracheostomy. Discussion: Polymyositis can rarely mimic ALS but this is, to our knowledge, the first report of cooccurrence of these two disorders. Muscle biopsy is required in order to confirm or discard this hypothesis. Moreover, albeit our case did not respond to treatment, a correct diagnosis could be extremely important due to the possible favourable response of polymyositis to steroids.