The basophilic inclusions described in juvenile onset motor neuron disease stain with p62. I.S. Scott1,2, S.M.L. Paine2 and J.S. Lowe2 Neuropathology Unit, Hull & East Yorkshire NHS Trust, Hull Royal Infirmary, Anlaby Road, Hull, HU3 2JZ, U.K. Department of Neuropathology, Nottingham University Teaching Hospitals NHS Trust, Queen’s Medical Centre Campus, Derby Road, Nottingham, NG7 2UH, U.K. Introduction: The presence of a classical motor neuron disease phenotype in the juvenile or young adult has a broad differential diagnosis that includes motor neuron disease with basophilic inclusions. Here, we report a case that was diagnosed post-mortem and adds to reports (1,2) confirming inclusion immunoreactivity with p62 (sequestosome-1). Case Presentation: An 18-year old male died from aspiration pneumonia shortly after presenting with a bulbar palsy. At necropsy there was marked muscle wasting with mild atrophy of the anterior nerve roots in the spinal cord. Histology: Histological sections showed mild myelin loss from the descending tracts with preservation of the dorsal funiculi. There was loss of a-motor neuron nuclei but only very occasional skein-like inclusions were seen on staining with ubiquitin antibodies. No characteristic ubiquitinated cytoplasmic inclusions were seen. In addition, despite the predominant bulbar clinical phenotype, no ubiquitinated inclusions were seen in the bulbar nuclei of the brain stem or in the dentate fascia of the hippocampus. There was no Lewy body or tangle pathology. Review of the haematoxylin & eosin-stained sections revealed cytoplasmic clumps of amorphous, basophilic material within the cytoplasm of neurons in the anterior horns of the spinal cord, brain stem cranial nerve nuclei (Fig. 1A) and the hippocampus. These inclusions were largely negative on staining with ubiquitin (Fig. 1B). The presence of cytoplasmic inclusions with this characteristic histological and immunocytochemical phenotype, in the presence of juvenile onset motor neuron disease, suggests the diagnosis of motor neuron disease with basophilic inclusions. Antibodies against p62 revealed dense staining of these characteristic inclusions despite there being virtually no expression of ubiquitin using polyclonal antibody known to be reactive against ubiquitin-protein conjugates (Fig. 2 A-D). Figure 1: The cytoplasmic inclusions are UQ-negative A B a-motor neurons in the spinal cord contain amorphous aggregates of basophilic material (A). Ubiquitin stains (B) reveal that ubiquitin is either absent or present at low levels in these inclusions. Figure 2: The aggregates contain p62 (sequestome-1) A B C D In contrast to ubiquitin, the basophilic inclusions contain dense deposits of p62. The pattern of staining varies to include well circumscribed cytoplasmic aggregates (A), flocculated clumps (B,C) and skein-like deposits (D). Conclusions: This case confirms the previously described p62 immunoreactivity of the basophilic inclusions of juvenile onset motor neuron disease and reinforces its use as a diagnostic aid. References: 1. Aizawa et al. Acta Neuropathologica 2000; 176:109-113. 2. Mizuno et al. Journal of Neurol. Sci. 2006; 249: 13-18.