Approach to hypohidrosis.

Hypohidrosis refers to diminished sweating in response to appropriate stimuli. This can cause hyperthermia, heat exhaustion and death. The aetiology of hypohidrosis can be divided into exogenous, dermatological and neurological causes. Exogenous causes act either by systemic neurohormonal inhibition of sweating or localised damage to the skin and sweat glands. Dermatological disorders can result from congenital disorders, wherein other ectodermal tissues may also be affected, or acquired disorders in which manifestations of the primary disease predominate. Neurological disorders should be classified based on an upper motor neuron or lower motor neuron pattern of disease. In the former, there is spasticity and hyperactive reflexes whereas in the latter, flaccidity and hypoactive reflexes predominate. Acquired idiopathic generalised anhidrois refers to isolated anhidrosis with no other detectable abnormalities. When approaching a patient with hypohidrois, exogenous causes should first be excluded. Physical examination, paying attention to mucocutaneous manifestations and neurological signs, will dichotomise if the lesion is dermatological or neurological. In the former, a skin biopsy is the investigation of choice. In the latter, one should consider magnetic resonance imaging of the brain and spinal cord for upper motor neuron lesions, nerve conduction tests for lower motor neuron lesions and autonomic nerve function tests for autonomic dysfunction. Finally, if a diagnosis of acquired idiopathic generalised anhidrosis is suspected, a quantitative sudomotor axon reflex test and serum immunoglobulin-E levels may be performed. Treatment involves addressing the underlying condition and avoidance of aggravating factors. Acquired idiopathic generalised anhidrosis responds well to high dose systemic corticosteroids.