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Damage of small nerve fibers may lead to a large variety of clinical symptoms. Small-fiber neuropathy underlies the symptoms of painful diabetic neuropathy, which may decrease quality of life. It also contributes to the poor prognosis of diabetic neuropathy because it plays a key role in the pathogenesis of foot ulceration and autonomic neuropathy. Impairment of small nerve fibers is considered the earliest alteration in the course of diabetic neuropathy. Therefore, assessment of functional and morphological abnormalities of small nerve fibers may enable timely diagnosis. The definition, symptoms, and clinical significance of small-fiber neuropathy are considered in the present review. An apparently more complex interaction between small-fiber impairment and microcirculation is extensively discussed. Diagnostic modalities include morphometric and functional methods. Corneal confocal microscopy and punch skin biopsy are considered gold standards, but noninvasive functional tests are also diagnostically useful. However, in routine clinical practice, small-fiber neuropathy is diagnosed by its typical clinical presentation. Finally, prompt treatment should be initiated following diagnosis.

In this issue of the journal, Gouveri et al report on olfactory dysfunction among patients with type 2 diabetes mellitus (T2DM) and raise the question whether it might be considered as an additional manifestation of microvascular disease. 1 Diagnostic methods to assess olfactory dysfunction are well established and validated: odor-dispensing devices, so-called ‘‘Sniffin’ Sticks,’’ are used and a total threshold–discrimination–identification (TDI) score is calculated. Age was negatively associated with the TDI score. After adjusting for age, gender, various risk factors, and cardiovascular disease, only T2DM and hypertension were associated with the TDI score. Olfactory dysfunction was associated with retinopathy and diabetic peripheral neuropathy. The latter finding should be considered particularly important. We agree with the authors that olfactory dysfunction may develop due to olfactory nerve impairment. This way, it should be regarded as a novel manifestation of central neuropathy. The term ‘‘diabetic neuropathy’’ refers to disorders of the peripheral nervous system due to neuropathy. However, we now know that dysfunction of the central nervous system is also present among diabetic patients. Cognitive impairment, 2 as well as depression, 3 is well recognized in diabetes. Cranial neuropathies are less frequent, most likely often overlooked, but well established manifestations of diabetic neuropathy. The impairment of cranial nerves is defined as a form of mononeuropathy. Cranial neuropathies are more frequent in older patients with long diabetes duration. Most of these patients have several comorbidities and their glycemic control is rather poor. 4 Isolated palsy of the third, fourth, or sixth cranial nerves is a characteristic manifestation of diabetic neuropathy. The presence of multiple, painless cranial nerve palsies in diabetic patients, even without other associated neurological deficits, may represent midbrain ischemia. 5 The incidence of cranial nerve involvement is 1% in diabetic patients. 6 Isolated third nerve palsies account for the majority of patients 4 and 11% of inpatients with third nerve palsy had diabetes. 7 The onset of cranial neuropathy is usually abrupt, with progression