Patients usually complain of progressive decline in functional ability in the right hand caused by decreased hand strength and dexterity. Such limitations may be manifested as decreased ability to complete daily self-care activities requiring a fine motor function such as eating, dressing, and grooming. Patients report that symptoms are worsened by cold temperatures. Rarely, symptoms will be reported with a triggering event. Depending on the time of presentation, patients already may have noted a decline in symptom progression.

Based on the rate of progression, initial presentation may be a complaint of deformity related to muscle atrophy. Sensory changes are rarely reported, and patients do not complain of pain until the atrophy has reached the upper arm and shoulder girdle, as seen in more severe cases.

The patient also may report increased fatigue and may have increased atopy or allergies. 

This constellation of symptoms causes patients to quit or decrease participation in sports and other activities. Such decreased activity or deformity may result in a change in socialization. 

Appearance

Common presentation is noted with gross deformity described as unilateral atrophy in the distal upper limb. Most atrophy occurs in the thenar, intrinsic hand muscles, hypothenar, and forearms. Depending on its severity, patients may also have limb length discrepancies.

Strength

Weakness noted in flexor and extensors of the wrist and digits based on the neural involvement of the C7-T1 nerve roots. Fine motor motions and grasp are limited by weakness, and patients may be unable to perform pinch or key grasp. Contralateral hand and digits remain at full strength and dexterity. Typically, elbow flexion, extension, pronation, and supination are unaffected. Generally, other proximal muscle groups are also spared.

Neurologic Exam

The sensory exam is intact for vibration, temperature, sharp, dull, and light touch on all extremities. Muscle stretch reflexes are generally normal and symmetric. Hoffman and Holman are noncontributory.

Cardiovascular

Pulses are present. Limbs are warm and have a good capillary refill.

Standards on physical examination were defined to help identify and diagnose this condition. These standards were described by Tashiro et al. as follows: 

• Predominant distal muscle weakness with hand and forearm atrophy. 
• Unilateral upper limbs almost always involved.
• Onset between the ages of 10 to early 20s. 
• Has sudden onset and gradual progression for several years, then stabilizes.
• No lower extremity involvement.
• No irregular sensory disturbances or tendon reflexes. 
• Other disease exclusion.[4]

Laboratory, imaging studies, and electromyogram (EMG)/nerve conduction study (NCS) studies are very helpful in distinguishing this process from other similar physical presentations. Routine blood work is noncontributory. Other blood tests, specifically serum IgE has shown a noted increase. However, the clinical significance of this finding is not known. Traditional x-rays also present with nonspecific findings. Occasionally, a degeneration of C2 may be noted.

MRI 

MRI tends to show some minor changes in structure that have been noted as a crescent-shaped lesion in the posterior epidural space of the lower cervical cord or an atrophic spinal cord, mild asymmetric cord flattening and increased signal intensity. It is only with specialized flexion MRIs that the etiology can be explained. Flexion MRIs have shown a distinct change in the alignment of the soft tissue structures, specifically an anterior shift of the cervical dural sac from the lamina at the C4 -C7 region allowing for chronic microtrauma, with a corresponding post contrast enhancement indicative of ischemia.

Electromyogram/Nerve Conduction Study

EMG and NCS significant findings are noted in the C7, C8 and T1 innervated muscles. NCS have intermittently demonstrated decreased compound muscle action potential (CMAP) amplitude most noticeable in the median nerve.

EMG findings are indicative of chronic denervation seen as a high amplitude of action potential with a prolonged duration, without active denervation (absence of positive sharp waves or fibrillation potentials) and no resting fasciculations in the C7, C8 and T1  innervated muscles. Findings are increased when the temperature is decreased.

Although considered to be a self-limited condition, the long-term effects warrant treatment. Conservative treatments are focused on decreasing the number or frequency of injuries. A cervical collar with the idea that decreased cervical movement and prevention of neck flexion is the first line of treatment. The protocol is to wear the collar for 3 to 4 years until growth spurts are completed, or expected plateau of the condition is seen. This treatment is focused on limiting the progression of symptoms.

For more advanced or severe presentations, surgical options may be recommended. Such patients will present with atypical muscular involvement and severe spinal cord atrophy seen on MRI. Surgical intervention (duroplasty with tenting) has been associated with an improved success rate and prognosis. Immediate effects of the procedure can be noted with an intraoperative ultrasound, demonstrating decreased spinal cord pulsation and increased amplitude of conductive spinal cord potentials noted after dural incision. Later, functional improvements are noted as increased hand strength following typical rehabilitation.

Myotonic dystrophy: An autosomal dominant genetic disorder, commonly seen in middle-aged men and traditionally identified with a tonic contraction of muscles in the upper limbs. It is associated with systemic changes including cataracts, pulmonary dysfunction, endocrine pathology, infertility, and cardiac conduction changes. It is distinguished from Hirayama by systemic involvement and EMG Findings, absent MRI findings and muscle biopsy findings.

Tephromalacie Anterieure: Anterior horn infarction demonstrated with muscle wasting of the distal upper limbs, caused by an occlusion of spinal arteries, commonly seen in middle-aged adults, and associated with arteriosclerosis. It presents bilaterally.

Syringomyelia: Chronic central degeneration associated with motor and sensory changes seen in bilateral upper limbs, commonly seen after injury in geriatric populations without preference to gender. Structural changes can be seen on imaging. 

Pronator syndrome: Commonly presents unilaterally and is associated with a chronic injury. Symptoms increase with specific activities. Increased reports of pain help to identify this condition with physical findings and also indicate more than one peripheral nerve involvement.

Hirayama disease has a good prognosis, in part due to its slow progression and expected plateau.

While considered to be a self-limited condition, with a plateau after a few years, some involved presentations may warrant a referral to occupational therapy for adaptive techniques to maintain independence and function which symptoms hinder or limit age-appropriate self-care and social interactions. Severe or rapidly progressing presentations also require a Neurosurgical consult to evaluate the stability of structures, monitor progression while providing conservative treatment to assess the need for definitive Surgical treatment.[4]