Systemic lupus erythematosus (SLE) is a chronic disease of connective tissue with multi-organ involvement. Manifestation in the nervous system is one of the most difficult symptoms to assess and interpret. The aim of the study is to indicate diagnostic problems in patients with SLE in whom neurological symptoms are present at the time of diagnosis of SLE but also with complications that occurred after diagnosis. In the presented case, the appearance of flaccid tetraparesis with areflexia suggested peripheral damage to the nervous system. In the electromyography performed in this patient, acute axonal polyneuropathy was mainly suspected. Further differential diagnosis should consider other acute and subacute developing polyneuropathies. Guillain-Barré polyneuropathy deserves special attention. To our knowledge, this is the first case documented in the literature of the coexistence of critical illness polyneuropathy and SLE.