Somatic symptom progression in idiopathic Parkinson's disease

The substantia nigra (SN) pars compacta is arranged somatotopically. Symptoms of idiopathic Parkinson's disease (IPD) are caused by a lesion in this nucleus, which spreads in a stereotyped spatio-temporal pattern during the course of the disease. We investigated the order of somatic symptom progression in a group of 30 patients with IPD to determine if progression of symptoms was consistent with ordered spread of pathology through the SN pars compacta. Thirty outpatients with IPD were interviewed retrospectively about the progression of their symptoms using a semi-structured questionnaire. All the patients experienced somatic symptom progression in one of two distinct patterns, which was dependent on the location of the initial symptom. The typical pattern of progression for patients with lower limb onset was: (i) foot, (ii) leg, (iii) arm, (iv) hand, (v) face, (vi) voice and (vii) swallowing. For patients whose first symptom was in the upper limb progression to the face and lower limbs occurred roughly simultaneously or sequentially, with the typical pattern of progression: (i) hand/arm, (ii) foot/leg and face, (iii) speech and (iv) swallowing. These patterns of disease progression may reflect two distinct patterns of neuropathology within the SN pars compacta. Although the sample size was relatively small, this is the first time this phenomenon has been described in a full-length article.