<unk>  is typically diagnosed clinically. A skin biopsy may be needed in unusual cases. If no clear cause is obvious, it may be necessary to search for one. Blood tests, an endoscopy, or X-rays may be required to eliminate the possibility of diabetes or cancer as the cause. On biopsy, hyperkeratosis, epidermal folding, leukocyte infiltration, and melanocyte proliferation may be seen. Differential diagnosis<unk>  should be distinguished from the casal collar appearing in pellagra. Classification<unk>  is conventionally divided into benign and malignant forms, although may be divided into syndromes according to cause: * Benign This may include obesity-related, hereditary, and endocrine forms of<unk> . * Malignant. This may include forms that are associated with tumour products and insulin-like activity, or tumour necrosis factor. An alternate classification system still used to describe<unk>  was proposed in 1994. It delineates<unk>  syndromes according to their associated syndromes, including benign and malignant forms, forms associated with obesity and drugs, acral<unk> , unilateral<unk> , and mixed and syndromic forms.
Acanthosis nigricans
Metabolic syndrome
Hypertrichosis
Green nails
Xanthosis
Blue nails
Hypertrichosis cubiti
Generalized lentiginosis