NQ-067: (B) These inclusions are specific for mitochondrial myopathy

Diagnosis: Dermatomyositis

Pathology of this case: This electron micrograph was taken from a muscle biopsy. These are the so-called parking-lot crystalloids that are classically associated with mitochondrial myopathy. However, one must know that it is not entirely specific. These inclusions can be seen in other conditions such as dermatomyositis. In fact, this electron micrograph is taken from a case of dermatomyositis.

Metachromatic leukodystrophy have prismatic inclusion, tuffstone inclusions and zebra bodies in the brain but not this type of inclusion.

McArdle’s disease has glycogen as the abnormal storage material.

Inclusion body myositis contains abnormal cytoplasmic, and less frequently nuclear, collections of abnormal filaments characterized by circular hollow profiles on cross section (on well oriented sections) and a rippled, and with periodic transverse striations, appearance on longitudinal sections. The cytoplasmic filaments (15-19 nm) tend to be larger than intranuclear filaments (12-15 nm). The filaments may be surrounded by membranous whorls.